Display-driving device and display-driving method performing gradation control based on a temporal modulation system

ABSTRACT

One selection period S and display cycles Td of a number corresponding to a maximum gradation level are allotted in one field, and the display cycle Td is composed of an unselection period U and a reset period R to perform the following control. A row electrode-driving circuit is used to output a selection pulse Ps during the selection period S, output an unselection signal Su during the unselection period U in the display cycle Td, and output a reset pulse Pr during the reset period R. A column electrode-driving circuit is used to output an ON signal during a light emission maintenance period, and output an OFF signal at least at an end timing of the light emission maintenance period, of the period other than the light emission maintenance period. Accordingly, it is possible to effectively reduce the electric power consumption, and it is possible to achieve the high brightness.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display-driving device and adisplay-driving method for driving a panel type display such as a liquidcrystal display, a plasma display, and a display for displaying apicture image corresponding to an image signal on an optical waveguideplate by controlling leakage light at a predetermined position of theoptical waveguide plate by controlling the displacement action of anactuator element in a direction to make contact or separation withrespect to the optical waveguide plate in accordance with an attributeof the image signal to be inputted (conveniently referred to as“electrostrictive type display”).

2. Description of the Related Art

Those hitherto known as displays include display devices such as cathoderay tubes (CRT), liquid crystal displays, and plasma displays.

Those known as the cathode ray tube include, for example, ordinarytelevision receivers and monitor units for computers. Although thecathode ray tube has a bright screen, it consumes a large amount ofelectric power. Further, the cathode ray tube involves a problem thatthe depth of the entire display device is large as compared with thesize of the screen. Further, for example, the cathode ray tube involvesdrawbacks in that the resolution is decreased in the circumferentialareas of the display images, the image or the graphic is distorted,there is no memory function, and it is impossible to present display ina large scale.

The reason for the foregoing phenomenon is as follows. That is, in thecase of the cathode ray tube, the electron beam emitted from theelectron gun is greatly deflected. Therefore, the light emission point(beam spot) is expanded at portions at which the electron beam reachesthe fluorescent screen of the Braun tube in an inclined manner, and thusthe image is displayed in an inclined manner. For this reason, strainoccurs on the display image. Moreover, there is a limit for themaintenance to keep a large space at the inside of a Braun tube to be ina vacuum.

On the other hand, the panel type display, for example, the liquidcrystal display is advantageous in that the entire device can beminiaturized, and the display consumes a small amount of electric power.The plasma display and the electrostrictive type display can beminiaturized, because the display section itself does not have a largevolume, in the same manner as the liquid crystal display as describedabove. They are advantageous in that there is no trouble in viewing thescreen, because the display surface is flat. Especially, the AC typeplasma display and the electrostrictive type display are alsoadvantageous in that the refresh memory is unnecessary owing to thememory function of the cell.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a display-drivingdevice and a display-driving method which make it possible toeffectively reduce electric power consumption and achieve highbrightness in a panel type display as described above.

Another object of the present invention is to provide a display-drivingdevice and a display-driving method which make it possible toeffectively reduce electric power consumption and achieve highbrightness in gradation control based on subfield driving.

Still another object of the present invention is to provide adisplay-driving device and a display-driving method which make itpossible to reduce the total number of subfields and effectively reduceelectric power consumption in gradation control based on subfielddriving.

According to the present invention, there is provided a display-drivingdevice for a display comprising a driving section including a largenumber of picture elements arranged in a matrix form for displaying apicture image corresponding to a supplied image signal; thedisplay-driving device comprising a first driving circuit for selectingthe picture elements at least in one row unit, a second driving circuitfor outputting display information composed of an ON signal and an OFFsignal to a selected row, and a signal control circuit for controllingthe first and second driving circuits; wherein assuming that a displayperiod for one image is one field in order to perform gradation controlbased on at least a temporal modulation system, the signal controlcircuit determines, in the one field, a light emission start timing anda light emission maintenance period having a variable length irrelevantto a selection/unselection state of the concerning picture elementdepending on a gradation level of the selected picture element.

Assuming that the display period for one image is one field, the lightemission start time of the concerning picture element and the lightemission maintenance period having the variable length irrelevant to theselection/unselection state of the concerning picture element aredetermined in the one field depending on the gradation level of theselected picture element, in accordance with the control performed bythe signal control circuit. Accordingly, the light emission is startedfor the concerning picture element substantially in synchronization withthe light emission start timing, and the light emission state ismaintained over the light emission maintenance period.

This arrangement makes it possible to effectively reduce the electricpower consumption as compared with other driving systems in which onefield is divided into a plurality of subfields, and forcible reset isperformed for each of the subfields (as adopted, for example, for theplasma display). Further, the light emission state is maintained overthe light emission maintenance period. Therefore, it is also possible torealize the improvement in brightness.

In the display-driving device constructed as described above, it is alsopreferable that one selection period and display cycles of a numbercorresponding to a maximum gradation level are allotted in the onefield; each of the display cycles is composed of an unselection periodand a reset period; and the signal control circuit is operated such thatthe concerning picture element is in a light emission state when the ONsignal indicating light emission is inputted during the selectionperiod, or the concerning picture element is in a light off state whenthe OFF signal indicating light off is inputted during the reset periodin the display cycle.

Accordingly, assuming that the selection period is allotted to the headof the one field, one display cycle is selected, or a plurality ofdisplay cycles are continuously selected from the head of the one fielddepending on the gradation level of the concerning picture element. TheON signal is outputted at the head of the selected display cycle, andthe OFF signal is outputted in the reset period of the display cyclenext to the selected display cycle. In other words, the head of theselected display cycle is the light emission start timing, and theperiod corresponding to the selected display cycle is the light emissionmaintenance period.

In this arrangement, only one cycle is used for the light emission andthe light off for the concerning picture element in the one field.Accordingly, it is possible to effectively reduce the electric powerconsumption. Further, the good linearity is obtained for the gradationand the brightness, and thus it is possible to make highly accurategradational expression. Furthermore, the efficiency of the lightemission time is also enhanced.

In the display-driving device constructed as described above, it is alsopreferable that signal levels are determined for the unselection periodand the reset period so that the light emission state of the concerningpicture element is maintained during the light emission maintenanceperiod; and signal levels are determined for the selection period andthe unselection period so that the light off state of the concerningpicture element is maintained during any period other than the lightemission maintenance period. In this arrangement, it is easy to achievethe maintenance of light emission during the light emission maintenanceperiod and the maintenance of light off during the period other than thelight emission maintenance period. Thus, it is possible to reliablyperform the cycle including only one time of light emission and lightoff in the one field as described above.

In the display-driving device constructed as described above, it is alsopreferable that display cycles of a number corresponding to a maximumgradation level and one reset period are allotted in the one field; eachof the display cycles is composed of a selection period and anunselection period; and the signal control circuit is operated such thatthe concerning picture element is in a light emission state when the ONsignal indicating light emission is inputted during the selectionperiod, or the concerning picture element is in a light off state duringthe reset period.

Accordingly, assuming that the reset period is allotted to the rear endof the one field, one display cycle is selected, or a plurality ofdisplay cycles are continuously selected from the rear end of the onefield depending on the gradation level of the concerning pictureelement. The ON signal is outputted at the head of the selected displaycycle, and the OFF signal is outputted in the reset period at the rearend.

Also in this arrangement, only one cycle is used for the light emissionand the light off for the concerning picture element in the one field.Accordingly, it is possible to effectively reduce the electric powerconsumption. Further, the good linearity is obtained for the gradationand the brightness, and thus it is possible to make highly accurategradational expression. Furthermore, the efficiency of the lightemission time is also enhanced. Especially, the brightness can besufficiently maintained over the light emission maintenance period forthe concerning picture element, because the selection period exists forevery selected display cycle.

In the display-driving device constructed as described above, it is alsopreferable that signal levels are determined for the selection periodand the unselection period so that the light emission state of theconcerning picture element is maintained during the light emissionmaintenance period. Accordingly, it is easy to achieve the maintenanceof light emission during the light emission maintenance period and themaintenance of light off during the period other than the light emissionmaintenance period. Thus, it is possible to reliably perform the cycleincluding only one time of light emission and light off in the onefield.

In the display-driving device constructed as described above, it is alsopreferable that an odd/even-adjusting cycle including a unit unselectionperiod having a predetermined length between two selection periods, anddisplay cycles of a number corresponding to a maximum gradation levelare allotted in the one field; and each of the display cycles isprovided with a redundant unselection period having a length which istwice the predetermined length and a reset period.

In this arrangement, for example, it is assumed that eight gradationsare expressed in the one field. If the one field is constructed by usingonly the unit display cycle, it is necessary to perform selectivescanning eight times for one row. However, when the display cycles, eachof which is provided with the redundant unselection period having thelength twice the predetermined length, are allotted, it is enough toperform selective scanning five times for one row. Thus, it is possibleto reduce the cycles (row scanning cycles) for selecting one row. Thisresults in the reduction of the electric power consumption.

Further, this also results in the high brightness of the selectedpicture element, because the light emission state is maintained duringthe redundant unselection period.

When the gradation level of the concerning picture element is odd, thelight emission start timing is set to be substantially insynchronization with the head selection period of the odd/even-adjustingcycle; while when the gradation level of the concerning picture elementis even, the light emission start timing is set to be substantially insynchronization with the rear end selection period of theodd/even-adjusting cycle.

In the display-driving device constructed as described above, it is alsopreferable that display cycles of a number corresponding to a maximumgradation level, and an odd/even-adjusting cycle including a unitunselection period having a predetermined length between two resetperiods are allotted in the one field; and each of the display cycles isprovided with a selection period and a redundant unselection periodhaving a length which is twice the predetermined length.

Also in this arrangement, it is possible to reduce the row scanningcycles as described above, and it is possible to reduce the electricpower consumption.

When the gradation level of the concerning picture element is odd, anend timing for the light emission maintenance period is set to besubstantially in synchronization with the terminal end reset period ofthe odd/even-adjusting cycle; while when the gradation level of theconcerning picture element is even, the end timing for the lightemission maintenance period is set to be substantially insynchronization with the head reset period of the odd/even-adjustingcycle.

In the display-driving device constructed as described above, it is alsopreferable that at least one unit display cycle including a unitunselection period having a predetermined length, and at least oneredundant display cycle are allotted in the one field; and the redundantdisplay cycle is provided with a redundant unselection period having alength which is n-times the predetermined length (n is an integer of notless than 2).

In this arrangement, for example, it is assumed that eight gradationsare expressed in the one field. It is enough to perform selectivescanning five times for one row. Thus, it is possible to greatly reducethe row scanning cycles. As a result, it is possible to realize thereduction of electric power consumption and the high brightness.

In the display-driving device constructed as described above, it is alsopreferable that the following expressions are satisfied:Z=(quotient of X/n)−1Y=X−Z×n[total number of subfields (Y+Z)=(X/n−1)+n]provided that a maximum gradation level is X, a number of unit displaycycles is Y, and a number of redundant display cycles is Z. In thisarrangement, the total number of subfield exactly corresponds to the rowscanning cycles described above. Therefore, a combination to minimizethe total number of subfields necessarily exists. When such acombination is adopted, then it is possible to reduce the electric powerconsumption more effectively, and it is possible to mitigate the load onthe scanning circuit.

Preferably, “a” individuals of selection periods are allotted to therespective display cycles from a head of the one field, and “b”individuals of reset periods are allotted to the respective displaycycles from a rear end of the one field; wherein the followingexpression is satisfied:a+b=Y+Z+1.Accordingly, it is possible to make a variety of gradationalexpressions. In this arrangement, in the case of b=n, all of thegradations included in the maximum gradation level can be expressed.However, assuming that there is given b=n−1, one or several gradationlevels may be curtailed. This reduces the row scanning cycles, and henceit is possible to realize the low electric power consumption.

In the display-driving device constructed as described above, it is alsopreferable that the unit display cycle and the redundant display cycleare allotted by using a combination which corresponds to a minimum totalnumber of subfields of total numbers of subfields corresponding to amaximum gradation level obtained by arbitrarily combining the unitdisplay cycle and the redundant display cycle.

For example, if the maximum gradation level is 16, the total number ofsubfields is 15 in the case of only the unit display cycle, 9 in thecase of a combination of the unit display cycle and the 2-fold redundantdisplay cycle, 7 in the case of a combination of the unit display cycleand the 4-fold redundant display cycle, or 9 in the case of acombination of the unit display cycle and the 8-fold redundant displaycycle. In this case, the combination of the unit display cycle and the4-fold redundant display cycle is selected, in which the total number ofsubfields is minimum.

As a result, it is possible to reduce the electric power consumptionmore effectively, and it is possible to mitigate the load on thescanning circuit as having been described above.

In the display-driving device constructed as described above, it is alsopreferable that the one field includes therein a first subfield blockcomposed of at least one redundant display cycle and a second subfieldblock composed of at least one unit display cycle; and a forcible resetperiod is provided between the first and second subfield blocks.

Owing to the use of the redundant display cycle in the first subfieldblock, it is possible reduce the number of row scanning cycles, and itis possible to realize the reduction of electric power consumption.Especially, owing to the provision of the forcible reset period, it ispossible to give a signal sufficient to quench the picture elementduring the period.

In the display-driving device constructed as described above, it is alsopreferable that the second subfield block is composed of at least oneredundant display cycle and at least one unit display cycle.

In this arrangement, it is also possible to reduce the number of rowscanning cycles in the second subfield block. Therefore, it is possibleto realize the further reduction of electric power consumption.

In the display-driving device constructed as described above, it is alsopreferable that the display comprises an optical waveguide plate forintroducing light thereinto, and the driving section provided opposinglyto one plate surface of the optical waveguide plate and including anumber of actuator elements arranged corresponding to the large numberof picture elements, for displaying, on the optical waveguide plate, thepicture image corresponding to the image signal by controlling leakagelight at a predetermined portion of the optical waveguide plate bycontrolling displacement action of each of the actuator elements in adirection to make contact or separation with respect to the opticalwaveguide plate in accordance with an attribute of the image signal tobe inputted.

In the present invention, it is desirable that the first and seconddriving circuits have the following features.

(1) The actuator element undergoes the capacitive load. Therefore,considering the fact that the capacitive load is subjected to thedriving, it is desirable that the partial voltage ratio, which isapplied to the capacitive load, is not less than 50%, for example, atthe time of completion of voltage (ON voltage) application for allowingthe actuator element to make the bending displacement.

(2) In order to obtain an displacement amount of the actuator elementwhich makes it possible to express the ON state and the OFF state of thepicture element, it is desirable that an voltage output of not less than20 V can be provided.

(3) It is desirable to consider the fact that the direction of theoutput current is recognized to be bidirectional.

(4) It is desirable that the load concerning the two-electrode structurein the row direction and the column direction can be subjected to thedriving.

Especially, it is also preferable that the actuator element comprises ashape-retaining layer, an operating section having at least a pair ofelectrodes formed on the shape-retaining layer, a vibrating section forsupporting the operating section, and a fixed section for supporting thevibrating section in a vibrating manner; wherein the display comprises adisplacement-transmitting section for transmitting the displacementaction of the actuator element to the optical waveguide plate, thedisplacement action being generated by voltage application to the pairof electrodes.

In the present invention, the term “actuator element having theshape-retaining layer” indicates an actuator element which has at leasttwo or more displacement states at an identical voltage level.

Accordingly, all of the light, which is introduced, for example, fromthe end of the optical waveguide plate, is totally reflected at theinside of the optical waveguide plate without being transmitted throughthe front and back surfaces of the optical waveguide plate (light offstate), by regulating the magnitude of the refractive index of theoptical waveguide plate. In this light off state, for example, when thedisplacement-transmitting section contacts with the back surface of theoptical waveguide plate at a distance of not more than the wavelength ofthe light, then the light, which has been totally reflected, istransmitted to the surface of the displacement-transmitting sectioncontacting with the back surface of the optical waveguide plate. Thelight, which has once reached the surface of thedisplacement-transmitting section, is reflected by the surface of thedisplacement-transmitting section, and the light behaves as scatteredlight. A part of the scattered light is reflected again at the inside ofthe optical waveguide plate. However, almost all of the scattered lightis not reflected by the optical waveguide plate, and the light istransmitted through the front surface of the optical waveguide plate(light emission state).

As described above, it is possible to control the presence or absence oflight emission (leakage light) at the front surface of the opticalwaveguide plate, depending on the presence or absence of the contact ofthe displacement-transmitting section disposed at the back of theoptical waveguide plate. In this case, one unit for allowing thedisplacement-transmitting section to make the displacement action in thedirection to give contact or separation with respect to the opticalwaveguide plate may be regarded as one picture element. Thus, a pictureimage (for example, characters and graphics) corresponding to an imagesignal can be displayed on the front surface of the optical waveguideplate in the same manner as in the cathode ray tube and the liquidcrystal display, by arranging a large number of such picture elements ina matrix form, and controlling the displacement action of each of thepicture elements in accordance with an attribute of the inputted imagesignal.

The actuator element having the shape-retaining layer has the followingfeatures.

(1) The threshold characteristic concerning the change from the lightoff state to the light emission state is steep as compared with the casein which no shape-retaining layer exists. Accordingly, it is possible tonarrow the deflection width of the voltage, and it is possible tomitigate the load on the circuit.

(2) The difference between the light emission state and the light offstate is distinct, resulting in improvement in contrast.

(3) The dispersion of threshold value is decreased, and an enough marginis provided for the voltage setting range.

It is desirable to use, as the actuator element, an actuator elementwhich makes, for example, upward displacement (giving the separatedstate upon no voltage load and giving the contact state upon voltageapplication) because of easiness of control. Especially, it is desirableto use an actuator element having a structure including a pair ofelectrodes on its surface. It is preferable to use, for example, apiezoelectric/electrostrictive layer and an anti-ferroelectric layer asthe shape-retaining layer.

In the display-driving device constructed as described above, it is alsopreferable that the driving section is formed with switching elementscorresponding to the actuator elements respectively; and thedisplacement action of the actuator element is controlled by means ofON/OFF control effected by the switching element.

Accordingly, the large number of arranged actuator elements are selectedin the unit of row on the basis of the input of the image signal, andthe display information (voltage signal) concerning the selected row issupplied.

Usually, the voltage signal is also supplied to the actuator elementsconcerning the unselected row irrelevant to the selected row. However,in the case of the display according to the present invention, theactuator elements concerning the unselected row are operated as follows.That is, the unselected row can be prevented from the supply of thedisplay information by turning off the corresponding switching elements.Accordingly, it is unnecessary to drive the picture elements (actuatorelements) concerning the unselected row. Thus, it is possible toeffectively reduce the electric power consumption.

The electrostatic capacity of the actuator element is small, and the CRtime constant depending on the wiring resistance and the switching ONresistance is small. Therefore, when the switching element is turned on,the actuator elements concerning the selected row are quickly charged.When the switching element is turned off thereafter, the connectedsection between the display information supply line (signal line) andthe actuator element is in a state of extremely high impedance, i.e., ina state approximately equivalent to the open state. This means the factthat the resistance becomes extremely large.

Therefore, the CR time constant also becomes extremely large.

Accordingly, even when the switching element is turned off, the supplyof the display information (application of the voltage signal) to theactuator element is maintained. Therefore, the concerning actuatorelement continuously maintains the displacement amount of not less thana certain amount. Thus, the ON state of the concerning picture elementis maintained.

As described above, the actuator element concerning the unselected rowis maintained in the open state while being charged. The displacementamount, which has been given upon the selection of the row, can bemaintained for a certain period of time in the state of being appliedwith no signal. Therefore, it is possible to effect the light emissionof the picture element during the unselection period. Accordingly, it ispossible to realize the high brightness.

The respective switching elements can be formed on the driving section(either on the principal surface or on the back surface thereof).Therefore, it is unnecessary to form any large wiring pattern on thedriving section. Thus, it is possible to simplify the wiringarrangement.

Unlike the liquid crystal display (TFT-LCD), the respective switchingelements can be installed in the space (at the place) irrelevant to theoptical path. The respective switching elements can be provided on theback surface of the driving section. Accordingly, it is possible toprovide a large numerical aperture of the picture element, and thus itis possible to improve the brightness.

It is preferable that the switching element is composed of a varistor.In this arrangement, an extremely excellent hysteresis characteristic isobtained when the actuator element is allowed to perform thedisplacement action. Thus, it is possible to obtain an memory effect asproviding the approximately complete shape maintenance.

According to another aspect of the present invention, there is provideda display-driving method for a display comprising a driving sectionincluding a large number of picture elements arranged in a matrix formfor displaying a picture image corresponding to a supplied image signal;the display-driving method comprising the steps of selecting the pictureelements at least in one row unit; outputting display informationcomposed of an ON signal and an OFF signal to a selected row; andperforming gradation control based on at least a temporal modulationsystem; wherein assuming that a display period for one image is onefield, a light emission start timing and a light emission maintenanceperiod having a variable length irrelevant to a selection/unselectionstate of the concerning picture element are determined in the one fielddepending on a gradation level of the selected picture element.

In this method, it is also preferable that one selection period anddisplay cycles of a number corresponding to a maximum gradation levelare allotted in the one field; each of the display cycles is composed ofan unselection period and a reset period; and the concerning pictureelement is in a light emission state when the ON signal indicating lightemission is inputted during the selection period; or the concerningpicture element is in a light off state when the OFF signal indicatinglight off is inputted during the reset period in the display cycle.

In this case, it is also preferable that signal levels are determinedfor the unselection period and the reset period so that the lightemission state of the concerning picture element is maintained duringthe light emission maintenance period; and signal levels are determinedfor the selection period and the unselection period so that the lightoff state of the concerning picture element is maintained during anyperiod other than the light emission maintenance period.

Further, it is also preferable that display cycles of a numbercorresponding to a maximum gradation level and one reset period areallotted in the one field; each of the display cycles is composed of a selection period and an unselection period; and the concerning pictureelement is in a light emission state when the ON signal indicating lightemission is inputted during the selection period; or the concerningpicture element is in a light off state during the reset period.

In this case, it is also preferable that signal levels are determinedfor the selection period and the unselection period so that the lightemission state of the concerning picture element is maintained duringthe light emission maintenance period.

In the method described above, it is also preferable that anodd/even-adjusting cycle including a unit unselection period having apredetermined length between two selection periods, and display cyclesof a number corresponding to a maximum gradation level are allotted inthe one field; and each of the display cycles is provided with aredundant unselection period having a length which is twice thepredetermined length and a reset period.

When the gradation level of the concerning picture element is odd, thelight emission start timing is set to be substantially insynchronization with the head selection period of the odd/even-adjustingcycle; while when the gradation level of the concerning picture elementis even, the light emission start timing is set to be substantially insynchronization with the rear end selection period of theodd/even-adjusting cycle.

In the method described above, it is also preferable that display cyclesof a number corresponding to a maximum gradation level, and anodd/even-adjusting cycle including a unit unselection period having apredetermined length between two reset periods are allotted in the onefield; and each of the display cycles is provided with a selectionperiod and a redundant unselection period having a length which is twicethe predetermined length.

When the gradation level of the concerning picture element is odd, anend timing for the light emission maintenance period is set to besubstantially in synchronization with the terminal end reset period ofthe odd/even-adjusting cycle; while when the gradation level of theconcerning picture element is even, the end timing for the lightemission maintenance period is set to be substantially insynchronization with the head reset period of the odd/even-adjustingcycle.

In the method described above, it is also preferable that at least oneunit display cycle including a unit unselection period having apredetermined length, and at least one redundant display cycle areallotted in the one field; and the redundant display cycle is providedwith a redundant unselection period having a length which is n-times thepredetermined length (n is an integer of not less than 2).

In this case, it is also preferable that the following expressions aresatisfied:Z=(quotient of X/n)−1Y=X−Z×n[total number of subfields (Y+Z)=(X/n−1)+n]provided that a maximum gradation level is X, a number of unit displaycycles is Y, and a number of redundant display cycles is Z.

It is also preferable that “a” individuals of selection periods areallotted to the respective display cycles from a head of the one field,and “b” individuals of reset periods are allotted to the respectivedisplay cycles from a rear end of the one field; wherein the followingexpression is satisfied:a+b=Y+Z+1.In this case, there may be given b=n, or b=n−1.

Especially, it is preferable that the unit display cycle and theredundant display cycle are allotted by using a combination whichcorresponds to a minimum total number of subfields of total numbers ofsubfields corresponding to a maximum gradation level obtained byarbitrarily combining the unit display cycle and the redundant displaycycle.

In the method described above, it is also preferable that the one fieldincludes therein a first subfield block composed of at least oneredundant display cycle and a second subfield block composed of at leastone unit display cycle; and a forcible reset period is provided betweenthe first and second subfield blocks.

In this case, it is also preferable that the second subfield block iscomposed of at least one redundant display cycle and at least one unitdisplay cycle.

In the driving method described above, it is also preferable that thegradation control is performed for the picture element by means ofON/OFF control effected by a switching element. In this case, it ispreferable that a varistor is used as the switching element.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which a preferredembodiment of the present invention is shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional arrangement illustrating a display towhich a driving device according to an embodiment of the presentinvention is applied;

FIG. 2 shows a view illustrating an example of a planar configuration ofa pair of electrodes formed on an actuator element;

FIG. 3A illustrates an example in which comb teeth of a pair ofelectrodes are arranged along a major axis of a shape-retaining layer;

FIG. 3B illustrates another example;

FIG. 4A illustrates an example in which comb teeth of a pair ofelectrodes are arranged along a minor axis of a shape-retaining layer;

FIG. 4B illustrates another example;

FIG. 5 shows an arrangement illustrating another example of a pair ofelectrodes formed on the actuator element;

FIG. 6 shows a magnified plan view illustrating an arrangement ofactuator elements (picture elements) included in the display;

FIG. 7 shows a bending displacement characteristic of the actuatorelement;

FIG. 8 shows an electric charge-applied voltage characteristic of theactuator element;

FIG. 9 shows an arrangement of the driving device according to theembodiment of the present invention;

FIG. 10 shows a cross-sectional arrangement illustrating a displayaccording to a first modified embodiment;

FIG. 11 shows a plan view illustrating an actuator element of thedisplay according to the first modified embodiment;

FIG. 12 shows an equivalent circuit concerning respective pictureelements arranged in a driving section of the display according to thefirst modified embodiment;

FIG. 13A shows a plan view illustrating an arrangement in which a pairof comb-shaped electrodes are formed on a shape-retaining layer of theactuator element of the display according to the first modifiedembodiment;

FIG. 13B shows a plan view illustrating an arrangement in which a pairof spiral-shaped electrodes are formed on a shape-retaining layer in thesame manner as described above;

FIG. 14 shows a plan view illustrating an arrangement in which a pair ofbranch-shaped electrodes are formed on a shape-retaining layer of theactuator element of the display according to the first modifiedembodiment;

FIG. 15 shows a cross-sectional arrangement illustrating a displayaccording to a second modified embodiment;

FIG. 16 shows a cross-sectional arrangement illustrating a displayaccording to a third modified embodiment;

FIG. 17 shows an equivalent circuit concerning respective pictureelements arranged in a driving section of a display according to afourth modified embodiment;

FIG. 18 shows a plan view illustrating an actuator element of thedisplay according to the fourth modified embodiment;

FIG. 19 shows a voltage-bending displacement characteristic of theactuator element of the display according to the fourth modifiedembodiment;

FIG. 20 shows an electric charge-applied voltage characteristic of theactuator element of the display according to the fourth modifiedembodiment;

FIG. 21 shows a bending displacement characteristic of a material havingno hysteresis;

FIG. 22A shows an example of an actuator element and a gate line formedon an actuator substrate;

FIG. 22B shows an example of a varistor and a data line formed on a backsurface side of an actuator substrate;

FIG. 23 illustrates an example of lamination of a varistor substrate toan actuator substrate;

FIG. 24A shows a plan view illustrating an arrangement in which a pairof comb-shaped electrodes are formed on a shape-retaining layer of theactuator element of the display according to the fourth modifiedembodiment;

FIG. 24B shows a plan view illustrating an arrangement in which a pairof spiral-shaped electrodes are formed on a shape-retaining layer;

FIG. 25 shows an equivalent circuit concerning respective pictureelements arranged in a driving section of a display according to a fifthmodified embodiment;

FIG. 26 shows a sectional view illustrating an actuator element and apiezoelectric relay of the display according to the fifth modifiedembodiment;

FIG. 27 shows a plan view illustrating the actuator element and thepiezoelectric relay of the display according to the fifth modifiedembodiment;

FIG. 28 shows a cross-sectional arrangement illustrating another exampleof the display according to the fifth modified embodiment;

FIG. 29 shows an example in which especially one field is equallydivided, for example, into a plurality of subfield in order toillustrate the gradation control based on the temporal modulationsystem;

FIG. 30A illustrates, for example, allotment of display cycles used in adriving system according to a first specified embodiment;

FIG. 30B shows signal waveforms illustrating the process for determiningthe light emission maintenance period concerning a picture element offirst row and first column;

FIG. 30C shows signal waveforms illustrating the process for determiningthe light emission maintenance period concerning a picture element ofsecond row and first column;

FIG. 31 shows an applied voltage waveform and a light intensitydistribution illustrating an experimental result obtained in accordancewith the driving system according to the first specified embodiment;

FIG. 32 shows an applied voltage waveform and a light intensitydistribution illustrating an experimental result obtained in accordancewith a driving system concerning a comparative example;

FIG. 33A illustrates, for example, allotment of display cycles used in adriving system according to a second specified embodiment;

FIG. 33B shows signal waveforms illustrating the process for determiningthe light emission maintenance period concerning a picture element offirst row and first column;

FIG. 33C shows signal waveforms illustrating the process for determiningthe light emission maintenance period concerning a picture element ofsecond row and first column;

FIG. 34 illustrates, for example, allotment of display cycles used in adriving system according to a third specified embodiment;

FIG. 35A illustrates, for example, allotment of display cycles used in adriving system according to a fourth specified embodiment;

FIG. 35B shows signal waveforms illustrating the process for determiningthe light emission maintenance period concerning a picture element offirst row and first column;

FIG. 35C shows signal waveforms illustrating the process for determiningthe light emission maintenance period concerning a picture element ofsecond row and first column;

FIG. 36A illustrates, for example, allotment of display cycles used in adriving system according to a fifth specified embodiment;

FIG. 36B shows signal waveforms illustrating the process for determiningthe light emission maintenance period concerning a picture element offirst row and first column;

FIG. 36C shows signal waveforms illustrating the process for determiningthe light emission maintenance period concerning a picture element ofsecond row and first column;

FIG. 37 illustrates, for example, allotment of display cycles used in adriving system according to a sixth specified embodiment;

FIG. 38 illustrates, for example, allotment of display cycles used in adriving system according to a seventh specified embodiment;

FIG. 39 shows a table illustrating the total number of subfieldscorresponding to the maximum gradation level obtain by arbitrarycombining the unit display cycle and the redundant display cycle;

FIG. 40 illustrates, for example, allotment of display cycles used in adriving system according to an eighth specified embodiment;

FIG. 41 illustrates, for example, allotment of display cycles used in adriving system according to a ninth specified embodiment;

FIG. 42 shows a table illustrating the relationship concerning, in thefirst to ninth specified embodiments, the selection pulse, theunselection signal, and the reset pulse outputted from the rowelectrode-driving circuit, the electric potentials of the ON signal andthe OFF signal outputted from the column electrode-driving circuit, andthe voltage applied between the row electrode and the column electrodeof each of the picture elements;

FIG. 43 shows a cross-sectional arrangement illustrating a displayaccording to a sixth modified embodiment;

FIG. 44 shows a table illustrating an example of the relationshipconcerning the selection pulse, the unselection signal, and the resetpulse outputted from the row electrode-driving circuit, the electricpotentials of the ON signal and the OFF signal outputted from the columnelectrode-driving circuit, and the voltage applied between the rowelectrode and the column electrode of each of the picture elements whenthe driving system concerning any of the first to ninth specifiedembodiments is applied to the display according to the sixth modifiedembodiment;

FIG. 45 shows a table illustrating another example of the relationshipconcerning the selection pulse, the unselection signal, and the resetpulse outputted from the row electrode-driving circuit, the electricpotentials of the ON signal and the OFF signal outputted from the columnelectrode-driving circuit, and the voltage applied between the rowelectrode and the column electrode of each of the picture elements whenthe driving system concerning any of the first to ninth specifiedembodiments is applied to the display according to the sixth modifiedembodiment;

FIG. 46 shows a frame response waveform obtained when the driving systemaccording to the second specified embodiment is applied to LCD based onthe simple matrix system to express the gradation level=7;

FIG. 47A shows a sectional view illustrating a light emission stateconcerning an example of a display based on the use of staticelectricity;

FIG. 47B shows a sectional view illustrating a light off stateconcerning the display described above;

FIG. 48A shows a sectional view illustrating a light emission stateconcerning another example of a display based on the use of staticelectricity; and

FIG. 48B shows a sectional view illustrating a light off stateconcerning the display described above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Illustrative embodiments of the display-driving device and thedisplay-driving method according to the present invention (hereinaftersimply referred to as “driving device according to the embodiment”) willbe explained below with reference to FIGS. 1 to 48B. Prior thereto,explanation will be made with reference to FIGS. 1 to 28 for thearrangement of the display to which the driving device according to theembodiment of the present invention is applied.

General Structure of Display

As shown in FIG. 1, the display D comprises an optical waveguide plate12 for introducing light 10 from a light source (not shown) thereinto,and a driving section 16 provided opposingly to the back surface of theoptical waveguide plate 12 and including a large number of actuatorelements 14 which are arranged corresponding to picture elements (imagepixels).

The display section 16 includes an actuator substrate 18 composed of,for example, ceramics. The actuator elements 14 are arranged atpositions corresponding to the respective picture elements on theactuator substrate 18. The actuator substrate 18 has its first principalsurface which is arranged to oppose to the back surface of the opticalwaveguide plate 12. The first principal surface is a continuous surface(flushed surface). Hollow spaces 20 for forming respective vibratingsections as described later on are provided at positions correspondingto the respective picture elements at the inside of the actuatorsubstrate 18. The respective hollow spaces 20 communicate with theoutside via through-holes 18a each having a small diameter and providedat a second principal surface of the actuator substrate 18.

The portion of the actuator substrate 18, at which the hollow space 20is formed, is thin-walled. The other portion of the actuator substrate18 is thick-walled. The thin-walled portion has a structure which tendsto undergo vibration in response to external stress, and it functions asa vibrating section 22. The portion other than the hollow space 20 isthick-walled, and it functions as a fixed section 24 for supporting thevibrating section 22.

That is, the actuator substrate 18 has a stacked structure comprising asubstrate layer 18A as a lowermost layer, a spacer layer 18B as anintermediate layer, and a thin plate layer 18C as an uppermost layer.The actuator substrate 18 can be recognized as an integrated structureincluding the hollow spaces 20 formed at the positions in the spacerlayer 18B corresponding to the picture elements. The substrate layer 18Afunctions as a substrate for reinforcement, as well as it functions as asubstrate for wiring. The actuator substrate 18 may be sintered in anintegrated manner, or it may be additionally attached.

As shown in FIG. 1, each of the actuator elements 14 comprises thevibrating section 22 and the fixed section 24 described above, as wellas a main actuator element 30 including a shape-retaining layer 26composed of, for example, a piezoelectric/electrostrictive layer or ananti-ferroelectric layer directly formed on the vibrating section 22 anda pair of electrodes 28 (a row electrode 28a and a column electrode 28b)formed on an upper surface of the shape-retaining layer 26, and adisplacement-transmitting section 32 connected onto the main actuatorelement 30 as shown in FIG. 1, for increasing the contact area withrespect to the optical waveguide plate 12 to obtain an areacorresponding to the picture element.

That is, the display D has the structure in which the main actuatorelements 30 comprising the shape-retaining layers 26 and the pairs ofelectrodes 28 are formed on the actuator substrate 18. The pair ofelectrodes 28 may have a structure in which they are formed on upper andlower sides of the shape-retaining layer 26, or they are formed on onlyone side of the shape-retaining layer 26. However, in order toadvantageously join the actuator substrate 18 and the shape-retaininglayer 26, it is preferable that the pair of electrodes 28 are formedonly on the upper side (the side opposite to the actuator substrate 18)of the shape-retaining layer 26 so that the actuator substrate 18directly contacts with the shape-retaining layer 26 without anydifference in height, as in the display D.

Explanation of Shapes and Related Matters of Respective ConstitutiveMembers

The shapes of the respective members are described in detail in JapaneseLaid-Open Patent Publication No. 10-578549. Therefore, they will bedescribed briefly herein.

At first, those adopted for the planar configurations of the vibratingsection 22 and the shape-retaining layer 26 include, for example,circular configurations, oblong circular configurations (track-shapedconfigurations), elliptic configurations, rectangular configurations(including configurations with rounded corners), and polygonalconfigurations (including, for example, octagonal configurations withrounded apex angles).

In this embodiment, the size of the vibrating section is the largest,and the outer circumferential configuration of the pair of electrodes 28is the second largest. The planar configuration of the shape-retaininglayer 26 is designed to be the smallest. Alternatively, it is allowablethat the outer circumferential configuration of the pair of electrodes28 is designed to be the largest.

The planar configuration of the pair of electrodes 28 (the row electrode28a and the column electrode 28b) may be a shape in which a large numberof comb teeth are opposed to one another in a complementary manner asshown in FIG. 2. Alternatively, it is possible to :adopt, for example, aspiral configuration and a branched configuration as disclosed inJapanese Laid-Open Patent Publication No. 10-78549 as well.

When the planar configuration of the shape-retaining layer 26 is, forexample, an elliptic configuration, and the pair of electrodes 28 areformed to have a comb teeth-shaped configuration, then it is possible toadopt, for example, a form in which the comb teeth of the pair ofelectrodes 28 are arranged along the major axis of the shape-retaininglayer 26 as shown in FIGS. 3A and 3B, and a form in which the comb teethof the pair of electrodes 28 are arranged along the minor axis of theshape-retaining layer 26 as shown in FIGS. 4A and 4B.

It is possible to adopt, for example, the form in which the comb teethof the pair of electrodes 28 are included in the planar configuration ofthe shape-retaining layer 26 as shown in FIGS. 3A and 4A, and the formin which the comb teeth of the pair of electrodes 28 protrude from theplanar configuration of the shape-retaining layer 26 as shown in FIGS.3B and 4B. The form shown in FIGS. 3B and 4B are more advantageous toeffect the bending displacement of the actuator element 14.

The pair of electrodes 28 may be arranged, for example, as follows asshown in FIG. 5. That is, for example, the row electrode 28a is formedon the lower surface of the shape-retaining layer 26, and the columnelectrode 28b is formed on the upper surface of the shape-retaininglayer 26.

In this embodiment, as shown in FIG. 1, it is possible that the actuatorelement 14 is allowed to make bending displacement in the firstdirection so that it is convex toward the optical waveguide plate 12.Alternatively, it is also possible that the actuator element 14 isallowed to make bending displacement in the second direction so that itis convex toward the hollow space 20.

The wiring arrangement communicating with the respective electrodes 28a,28b will be explained on the basis of an example shown in FIG. 6. Thatis, the wiring arrangement includes vertical selection lines 40 having anumber corresponding to a number of rows of a large number of thepicture elements, and signal lines 42 having a number corresponding to anumber of columns of the large number of the picture elements.

Each of the vertical selection lines 40 is electrically connected to therow electrode 28a of each of the picture elements (actuator elements 14,see FIG. 1). Each of the signal lines 42 is electrically connected tothe column electrode 28b of each of the picture elements 14. Therespective vertical selection lines 40, which are included in one row,are wired in series such that the wiring is led from the row electrode28a provided for the picture element in the previous column, and thenthe wiring is connected to the row electrode 28a provided for thepicture element in the present column. The signal line 42 comprises amain line 42a extending in the direction of the column, and branch lines42b branched from the main line 42a and connected to the columnelectrode 28b of each of the picture elements 14.

The voltage signal is supplied to the respective vertical selectionlines 40 from an unillustrated wiring board (stuck to the secondprincipal surface of the substrate 18) via through-holes 44. The voltagesignal is also supplied to the respective signal lines 42 from theunillustrated wiring board via through-holes 46.

The through-hole 44 for the vertical selection line 40 is not formed onthe vertical selection line 40, unlike the through-hole 46 for thesignal line 42. Accordingly, a mediating conductor 48 is formed betweenthe through-hole 44 and one of the electrodes 28a, for making electriccontinuity therebetween.

Insulative films 50 (shown by two-dot chain lines), each of which iscomposed of, for example, a silicon oxide film, a glass film, or a resinfilm, are allowed to intervene at portions of intersection between therespective vertical selection lines 40 and the respective signal lines42, in order to ensure insulation between the mutual wiring arrangements40, 42.

The configuration of the vibrating section 22, the planar configurationof the shape-retaining layer 26, and the outer circumferentialconfiguration formed by the pair of electrodes 28 may be combinations ofcircular and elliptic configurations, or combinations of rectangular andelliptic configurations, without any special limitation.

Although not shown, those preferably adopted as the planar configurationof the shape-retaining layer 26 include a ring-shaped configuration. Inthis case, those usable as the outer circumferential configurationinclude various ones such as circular, elliptic, and rectangularconfigurations. The ring-shaped planar configuration of theshape-retaining layer 26 makes it unnecessary to form any electrode onthe hollow portion. Therefore, it is possible to decrease theelectrostatic capacity without decreasing the displacement amount.

In the illustrative arrangement shown in FIG. 6, the respective actuatorelements 14 (picture elements) are illustratively arranged in the matrixform on the actuator substrate 18. Alternatively, it is also preferablethat the picture elements (actuator elements) 14 are arranged in azigzag form with respect to the respective rows.

Explanation of Shape-Retaining Layer

By the way, when the piezoelectric/electrostrictive layer is used as theshape-retaining layer 26, those usable as thepiezoelectric/electrostrictive layer include ceramics containing, forexample, lead zirconate, lead magnesium niobate, lead nickel niobate,lead zinc niobate, lead manganese niobate, lead magnesium tantalate,lead nickel tantalate, lead antimony stannate, lead titanate, bariumtitanate, lead magnesium tungstate, and lead cobalt niobate, as well asany combination of them. It is needless to say that the major componentcontains the compound as described above in an amount of not less than50% by weight. Among the ceramics described above, the ceramicscontaining lead zirconate is most frequently used as the constitutivematerial of the piezoelectric/electrostrictive layer according to theembodiment of the present invention.

When the piezoelectric/electrostrictive layer is composed of ceramics,it is also preferable to use ceramics obtained by appropriately adding,to the ceramics described above, oxide of, for example, lanthanum,calcium, strontium, molybdenum, tungsten, barium, niobium, zinc, nickel,and manganese, or any combination thereof or another type of compoundthereof. For example, it is preferable to use ceramics containing amajor component composed of lead magnesium niobate, lead zirconate, andlead titanate and further containing lanthanum and strontium.

The piezoelectric/electrostrictive layer may be either dense or porous.When the piezoelectric/electrostrictive layer is porous, its porosity ispreferably not more than 40%.

When the anti-ferroelectric layer is used as the shape-retaining layer26, it is desirable to use, as the anti-ferroelectric layer, a compoundcontaining a major component composed of lead zirconate, a compoundcontaining a major component composed of lead zirconate and leadstannate, a compound obtained by adding lanthanum to lead zirconate, anda compound obtained by adding lead zirconate and lead niobate to acomponent composed of lead zirconate and/or lead stannate.

Especially, when an anti-ferroelectric film, which contains a componentcomprising lead zirconate and lead stannate as represented by thefollowing composition, is applied as a film-type element such as theactuator element 14, it is possible to perform driving at a relativelylow voltage. Therefore, application of such an anti-ferroelectric filmis especially preferred.Pb_(0.99)Nb_(0.02)[(Zr_(x)Sn_(1-x))_(1-y)Ti_(y)]_(0.98)O₃wherein, 0.5<x<0.6, 0.05<y<0.063, 0.01<Nb<0.03

The anti-ferroelectric layer may be porous. When the anti-ferroelectriclayer is porous, it is desirable that the porosity is not more than 30%.

Those usable as the method for forming the shape-retaining layer 26 onthe vibrating section 22 include various types of the thick filmformation method such as the screen printing method, the dipping method,the application method, and the electrophoresis method, and varioustypes of the thin film formation method such as the ion beam method, thesputtering method, the vacuum evaporation method, the ion platingmethod, the chemical vapor deposition method (CVD), and the plating.

In this embodiment, when the shape-retaining layer 26 is formed on thevibrating section 22, the thick film formation method is preferablyadopted, based on, for example, the screen printing method, the dippingmethod, the application method, and the electrophoresis method.

In the techniques described above, the shape-retaining layer 26 can beformed by using, for example, paste, slurry, suspension, emulsion, orsol containing a major component of piezoelectric ceramic particleshaving an average grain size of 0.01 to 5 μm, preferably 0.05 to 3 μm,in which it is possible to obtain good piezoelectric operationcharacteristics.

Especially, the electrophoresis method makes it possible to form thefilm at a high density with a high shape accuracy, and it further hasthe features as described in technical literatures such as Anzai, Kazuo,“Preparation of Electronic Materials by Electrophoretic Deposition,”General Institute of Toshiba Corporation, Denki Kagaku 53, No. 1, 1985,pp. 63-68, Goto, Atsushi, et al., “PbZrO₃/PbTiO₃, Composite CeramicsFabricated by Electrophoretic Deposition,” Tokyo MetropolitanUniversity, Tokyo Medical and Dental University, Proceedings of FirstSymposium on Higher-Order Ceramic Formation Method Based onElectrophoresis, 1998, pp. 5-6, and Yamashita, Kimihiro, “Hybridizationof Ceramics by Electrophoretic Deposition,” Institute of Medical andDental Engineering, Tokyo Medical and Dental University, Proceedings ofFirst Symposium on Higher-Order Ceramic Formation Method Based onElectrophoresis, 1998, pp. 23-24. Therefore, the technique may beappropriately selected and used considering, for example, the requiredaccuracy and the reliability.

Explanation of Operation of Display

Next, the operation of the display D constructed as described above willbe briefly described with reference to FIG. 1. At first, the light 10 isintroduced, for example, from the end portion of the optical waveguideplate 12. In this embodiment, all of the light 10 is totally reflectedat the inside of the optical waveguide plate 12 without beingtransmitted through the front and back surfaces thereof by controllingthe magnitude of the refractive index of the optical waveguide plate 12.In this state, when a certain actuator element 14 is in the selectedstate, and the displacement-transmitting section 32 corresponding to theactuator element 14 contacts, at a distance of not more than thewavelength of light 10, with the back surface of the optical waveguideplate 12, then the light 10, which has been totally reflected until thattime, is transmitted to the surface of the displacement-transmittingsection 32 contacting with the back surface of the optical waveguideplate 12.

The light 10, which has once arrived at the surface of thedisplacement-transmitting section 32, is reflected by the surface of thedisplacement-transmitting section 32, and it behaves as scattered light52. A part of the scattered light 52 is reflected again in the opticalwaveguide plate 12. However, almost all of the scattered light 52 is notreflected by the optical waveguide plate 12, and it is transmittedthrough the front surface of the optical waveguide plate 12.

That is, the presence or absence of light emission (leakage light) atthe front surface of the optical waveguide plate 12 can be controlleddepending on the presence or absence of the contact of thedisplacement-transmitting section 32 disposed at the back of the opticalwaveguide plate 12. Especially, In the display according to theembodiment of the present invention, one unit for making thedisplacement action of the displacement-transmitting section 32 in thedirection to make contact or separation with respect to the opticalwaveguide plate 12 may be recognized as one picture element. A largenumber of the picture elements are arranged in a matrix configuration orin a zigzag configuration concerning the respective rows. Therefore, itis possible to display a picture image (characters and graphics)corresponding to the image signal on the front surface of the opticalwaveguide plate in the same manner as in the cathode ray tube, theliquid crystal display device, and the plasma display, by controllingthe displacement action in each of the picture elements in accordancewith the attribute of the inputted image signal.

Principle of Operation of Actuator Element

Next, the principle of operation in the respective actuator elements 14,which is effected when the piezoelectric layer is used as theshape-retaining layer 26, will be explained on the basis of the bendingdisplacement characteristic shown in FIG. 7 and the electriccharge-applied voltage characteristic shown in FIG. 8.

The bending displacement characteristic shown in FIG. 7 is obtained byobserving the bending displacement of the actuator element 14 whilecontinuously changing the voltage applied to the actuator element 14. Inthis embodiment, as shown in FIG. 1, the direction of bendingdisplacement is positive when the actuator element, 14 makes bendingdisplacement in a first direction (direction to make approach to theoptical waveguide plate 12).

The electric charge-applied voltage characteristic shown in FIG. 8 isobtained by observing the change in amount of electric charge Qaccumulated between the pair of electrodes 28a, 28b of the actuatorelement 14 while continuously changing the voltage applied to theactuator element 14 as well. In the display D shown in FIG. 1, the pairof electrodes 28a, 28b are connected as follows as explained withreference to FIG. 6. That is, the vertical selection line 40 isconnected to the row electrode 28a, and the signal line 42 is connectedto the column electrode 28b. Therefore, the applied voltage indicatedalong the horizontal axis in FIGS. 7 and 8 represents the voltagebetween the vertical selection line 40 and the signal line 42 relativeto the concerning actuator element 14.

The measurement of the bending displacement characteristic will bespecifically explained with reference to an example. At first, a sinewave having a frequency of 1 kHz, a positive peak voltage of 180 V, anda negative peak voltage of −60 v is applied between the pair ofelectrodes 28a, 28b of the actuator element 14. The displacement amounton this condition is continuously measured at respective points (Point Ato Point H) by using a laser displacement meter. FIG. 7 shows thebending displacement characteristic obtained on this condition byplotting results of the measurement on the graph of voltage-bendingdisplacement. As indicated by arrows in FIG. 7, the displacement amountof the bending displacement continuously changes in accordance with thecontinuous increase and decrease in applied voltage while providing acertain degree of hysteresis. As shown in FIG. 8, the amount of electriccharge Q accumulated by the pair of electrodes 28a, 28b alsocontinuously changes in accordance with the continuous increase anddecrease in applied voltage while providing a certain degree ofhysteresis, in the same manner as in the characteristic shown in FIG. 7.

Specifically, at first, it is assumed that the measurement is startedfrom a no-voltage-loaded state (applied voltage=0 V) indicated by PointB. At Point B, no elongation occurs in the shape-retaining layer 26, andthe displacement-transmitting section 32 and the optical waveguide plate12 are in a separated state, i.e., in the light off state. The amount ofelectric charge Q is at the lowest level as well.

Next, when the positive peak voltage (=180 V) is applied between thepair of electrodes 28a, 28b of the actuator element 14, then theshape-retaining layer 26 is elongated in accordance with the increase inamount of electric charge Q as shown by Point E, and the actuatorelement 14 makes bending displacement in the first direction (thedirection to make approach to the optical waveguide plate 12). At thistime, the amount of electric charge Q is at the maximum level. Theconvex deformation of the actuator element 14 allows thedisplacement-transmitting section 32 to make displacement toward theoptical waveguide plate 12, and the displacement-transmitting section 32contacts with the optical waveguide plate 12.

The displacement-transmitting section 32 contacts with the back surfaceof the optical waveguide plate 12 in response to the bendingdisplacement of the actuator element 14. When thedisplacement-transmitting section 32 contacts with the back surface ofthe optical waveguide plate 12, for example, the light 10, which hasbeen totally reflected in the optical waveguide plate 12, is transmittedthrough the back surface of the optical waveguide plate 12, and it istransmitted to the surface of the displacement-transmitting section 32.The light 10 is reflected by the surface of thedisplacement-transmitting section 32. Accordingly, the picture elementcorresponding to the concerning actuator element 14 is in the lightemission state.

The displacement-transmitting section 32 is provided to reflect thelight transmitted through the back surface of the optical waveguideplate 12. Specifically, the displacement-transmitting section 32 isprovided to increase the contact area with respect to the opticalwaveguide plate 12 to be not less than a predetermined size. That is,the light emission area is determined by the contact area between thedisplacement-transmitting section 32 and the optical waveguide plate 12.

In the display D described above, the displacement-transmitting section32 includes the plate member 32a for determining the substantial lightemission area, and the displacement-transmitting member 32b fortransmitting the displacement of the main actuator element 30 to theplate member 32a.

The contact between the displacement-transmitting section 32 and theoptical waveguide plate 12 means the fact that thedisplacement-transmitting section 32 and the optical waveguide plate 12are positioned at a distance of not more than the wavelength of thelight 10 (light 10 introduced into the optical waveguide plate 12).

It is preferable that portions other than the plate member 32a whichmakes contact with the optical waveguide plate 12 are covered with ablack matrix formed by a metal film or a film containing carbon black,black pigment, or black dye. Especially, it is preferable to use, forexample, a metal film such as those made of Cr, Al, Ni, and Ag as theblack matrix, because of the following reason. That is, such a metalfilm absorbs a small amount of light, and hence it is possible tosuppress attenuation and scattering of the light transmitted through theoptical waveguide plate 12. Therefore, such a metal film is usedespecially preferably. Alternatively, when a film containing carbonblack, black pigment, or black dye is used as the black matrix, then thelight-absorbing performance is excellent, and it is possible to improvethe contrast.

Next, when the voltage application to the pair of electrode 28a, 28b ofthe actuator element 14 is stopped to give the no-voltage-loaded state,the actuator element 14 intends to make restoration from the convexstate to the original state (state indicated by Point B). However, dueto the hysteresis characteristic, the actuator element 14 does notundergo complete restoration to the state of Point B, and it gives astate in which it is slightly displaced in the first direction fromPoint B (state indicated by Point H). In this state, thedisplacement-transmitting section 32 and the optical waveguide plate 12are in a state in which they are separated from each other, i.e., in thelight off state.

Next, when the negative peak voltage (−60 V) is applied between the pairof electrode 28a, 28b of the actuator element 14, the shape-retaininglayer 26 is contracted as shown by Point A. Accordingly, the slightdisplacement in the first direction in the no-voltage-loaded state iscounteracted, and the actuator element 14 completely makes restorationto the original state.

As also understood from the characteristic curves shown in FIGS. 7 and8, the light emission state is maintained owing to the memory function(hysteresis characteristic) of the shape-retaining layer 26 even whenthe applied voltage is lowered, for example, up to +20 V to +100 V aftergiving the light emission state by applying the positive peak voltage(+180 V) between the pair of electrodes 28a, 28b. The memory function isalso effected in the light off state in the same manner as describedabove. The light off state is maintained owing to the memory function(hysteresis characteristic) of the shape-retaining layer 26 even whenthe applied voltage is raised, for example, up to +20 V to +100 V aftergiving the light off state by applying, for example, 0 V or the negativepeak voltage (−60 V) between the pair of electrodes 28a, 28b.

That is, the actuator element 14 having the shape-retaining layer 26 canbe defined as an actuator element 14 which has at least two or moredisplacement states at an identical voltage level.

The actuator element 14 having the shape-retaining layer 26 has thefollowing features.

(1) The threshold characteristic concerning the change from the lightoff state to the light emission state is steep as compared with the casein which no shape-retaining layer 26 exists. Accordingly, it is possibleto narrow the deflection width of the voltage, and it is possible tomitigate the load of the circuit.

(2) The difference between the light emission state and the light offstate is distinct, resulting in improvement in contrast.

(3) The dispersion of threshold value is decreased, and an enough marginis provided for the voltage setting range.

It is desirable to use, as the actuator element 14, an actuator element14 which makes, for example, upward displacement (giving the separatedstate upon no voltage load and giving the contact state upon voltageapplication) because of easiness of control. Especially, it is desirableto use the structure having the pair of electrodes 28a, 28b on thesurface.

Explanation of Driving Device

Next, explanation will be made for a driving device 200 according to theembodiment of the present invention with reference to FIG. 9. Thedriving device 200 comprises a row electrode-driving circuit 202 forselectively supplying a row signal SR to the vertical selection lines 40(connected in series to the row electrodes 28a of the actuator elements14 for the respective rows) for the driving section 16 comprising alarge number of actuator elements 14 arranged in the matrixconfiguration or in the zigzag configuration so that the actuatorelements 14 are successively selected in one row unit, a columnelectrode-driving circuit 204 for outputting a data signal SD inparallel to the signal lines 42 for the driving section 16 so that thedata signal SD is supplied to the column electrodes 28b of therespective actuator elements 14 on the row (selected row) selected bythe row electrode-driving circuit 202 respectively, and a signal controlcircuit 206 for controlling the row electrode-driving circuit 202 andthe column electrode-driving circuit 204 on the basis of a picture imagesignal Sv and a synchronization signal Ss to be inputted.

A logic power source voltage (for example, ±5 V) for logical operationperformed in an internal logic circuit, and three types of row sidepower source voltages (for example, −100 V, −20 V, and +60 V) forgenerating the row signal SR are supplied to the row electrode-drivingcircuit 202 by the aid of an unillustrated power source circuit. Thelogic power source voltage and two types of column side power sourcevoltages (for example, 80 V and 0 V) for generating the data signal SDare supplied to the column electrode-driving circuit 204 by the aid ofthe unillustrated power source circuit.

In this embodiment, the three types of the row side power sourcevoltages are used as follows. That is, the voltage of −100 V is used asa peak voltage of the selection pulse Ps as described later on, thevoltage of −20 V is used as a peak voltage of the unselection signal Su,and the voltage of 60 V is used as a peak voltage of the reset pulse Pr.Further, the two types of the column side power source voltages are usedas follows. That is, the voltage of 80 V is used as a peak voltage ofthe ON signal as described later on, and the voltage of 0 V is used as apeak voltage of the OFF signal.

The signal control circuit 206 comprises, at its inside, a timingcontroller, a frame memory, and an I/O buffer, which is constructed suchthat the row electrode-driving circuit 202 and the columnelectrode-driving circuit 204 are subjected to the gradation control onthe basis of the temporal modulation system via a row side control line208 communicating with the row electrode-driving circuit 202 and acolumn side control line 210 communicating with the columnelectrode-driving circuit 204.

It is desirable that the row electrode-driving circuit 202 and thecolumn electrode-driving circuit 204 have the following features.

(1) The actuator element 14 undergoes the capacitive load. Therefore,considering the fact that the capacitive load is subjected to thedriving, for example, it is desirable that the partial voltage ratio,which is applied to the capacitive load; is not less than 50% at thetime of completion of voltage (ON voltage) application for allowing theactuator element 14 to make the bending displacement.

(2) In order to obtain an displacement amount of the actuator element 14which makes it possible to express the light emission state and thelight off state of the picture element, it is desirable that an voltageoutput of not less than 20 V can be provided.

(3) It is desirable to consider the fact that the direction of theoutput current is recognized to be bidirectional.

(4) It is desirable that the load concerning the two-electrode structurein the row direction and the column direction can be subjected to thedriving.

Modified Embodiments of Display

Next, several modified embodiments of the display D will be explainedwith reference to FIGS. 10 to 28. Components or parts corresponding tothose shown in FIG. 1 are designated by the same reference numerals,duplicate explanation of which will be omitted.

At first, as shown in FIG. 10, a display Da according to a firstmodified embodiment is constructed in approximately the same manner asthe display D shown in FIG. 1. However, the former is different from thelatter in that an upper electrode 28a is formed on the upper surface ofthe shape-retaining layer 26 and a lower electrode 28b is formed on thelower surface of the shape-retaining layer 26, and in that a switchingTFT (thin film transistor) 60 is formed in the vicinity of each of theactuator elements 14 on the actuator substrate 18 (see FIG. 10,.) asshown in FIG. 11. In this modified embodiment, the upper electrode 28aof each of the actuator elements 14 is electrically connected via acontact 64 to a source/drain region 62 of the corresponding TFT 60.

As shown in FIG. 11, any one of the planar configuration of the upperelectrode 28a (see solid lines), the planar configuration of theshape-retaining layer 26 (see dashed lines), and the outercircumferential configuration of the lower electrode 28b (see brokenlines) is rectangular. In this modified embodiment, the size of theupper electrode 28a is designed to be the largest. The planarconfiguration of the shape-retaining layer 26 is designed to be thesecond largest. The planar configuration of the lower electrode 28b isdesigned to be the smallest.

As shown in FIGS. 11 and 12, each of the vertical selection lines 40 iselectrically connected via a contact 66 to the gate electrode of TFT 60formed corresponding to each of the picture elements (actuator elements)14. Each of the signal lines 42 is electrically connected via a contact70 to the source/drain region 68 of TFT 60 formed corresponding to eachof the picture elements 14.

An insulating film 72, which is composed of, for example, a siliconoxide film, a glass film, or a resin film, is allowed to intervene atthe portion of intersection of each of the vertical selection lines 40and each of the signal lines 42 in order to effect mutual insulation forthe wirings 40, 42.

The lower electrode 28b of each of the actuator elements 14 is led tothe back surface side of the actuator substrate 18 via a through-hole 74formed through the actuator substrate 18, and it is electricallyconnected to a ground line 76 (see FIG. 10) formed on the back surfaceof the actuator substrate 18.

Therefore, when one row is selected by the row electrode-driving circuit202, all of TFT's 60 concerning the selected row are turned on.Accordingly, the data signal, which is supplied by the columnelectrode-driving circuit 204, is supplied via the channel region of TFT60 to the upper electrode 28a of the actuator element 14.

In the display Da according to the first modified embodiment, TFT 60,which is the switching element for performing ON/OFF control of thevoltage application to each of the actuator elements 14, is providedcorresponding to each of the actuator elements 14. Therefore, the supplyof the data signal (the operation voltage and the reset voltage) to theunselected row can be avoided by turning off TFT 60 corresponding to theactuator element 14 concerning the unselected row. It is unnecessary todrive the picture element (actuator element) 14 concerning theunselected row. Thus, it is possible to effectively reduce the electricpower consumption.

Even when TFT 60 is turned off, the supply of the data signal(application of the operation voltage or the reset voltage) to theactuator element 14 is maintained. Accordingly, the concerning actuatorelement 14 continuously maintains the displacement amount which is notless than a certain amount. Thus, the ON state or the OFF state of theconcerning picture element is maintained.

As described above, the actuator element 14 concerning the unselectedrow is maintained in the open state while being charged, and thedisplacement amount, which is given when the row selection is performed,can be maintain for a certain period of time in the state of beingapplied with no signal. Accordingly, the light emission of the pictureelement can be effected during the unselection period. Therefore, it ispossible to realize the high brightness.

In the display Da according to the first modified embodiment, TFT 60 isformed on the actuator substrate 18 in the vicinity of each of theactuator elements 14. Therefore, it is unnecessary to form any largewiring pattern on the actuator substrate 18. Thus, it is possible tosimplify the wiring arrangements.

In the display Da according to the first modified embodiment, theactuator element 14, TFT 60, the vertical selection line 40, and thesignal line 42 are formed on the actuator substrate 18. The ground line76 is formed on the back surface side of the actuator substrate 18.Alternatively, it is also preferable that the actuator element 14 andthe ground line 74 are formed on the actuator substrate 18, and TFT 60,the vertical selection line 40, and the signal line 42 are formed on theback surface side of the actuator substrate 18.

In the display Da according to the first modified embodiment, the upperelectrode 28a and the lower electrode 28b are formed on the uppersurface and the lower surface of the shape-retaining layer 26.Alternatively, as shown in FIG. 1, it is also preferable that theshape-retaining layer 26 is directly formed on the vibrating section 22,and the pair of electrodes 28 are formed on the upper surface of theshape-retaining layer 26.

In this arrangement, the pair of electrodes 28a, 28b may have aconfiguration of comb teeth arranged alternately as shown in FIG. 13A.The pair of electrodes 28a, 28b may have a spiral configuration in whichthey are arranged in parallel to one another and separated from eachother as shown in FIG. 13B. Alternatively, the pair of electrodes 28a,28b may have a configuration (branched configuration) in which they areseparated from each other and arranged complementarily as shown in FIG.14. FIG. 14 is illustrative of the case in which the switching element(not shown) is formed on the back surface of the actuator substrate 18(see FIG. 1), and one of the electrodes 28a is electrically connected tothe switching element via the mediating conductor 78 and thethrough-hole 74.

The displays D, Da shown in FIGS. 1 and 10 are illustrative of the casein which the displacement-transmitting member 32b of thedisplacement-transmitting section 32 is formed in the film form over theentire surface. Alternatively, as in displays Db and Dc according tosecond and third modified embodiments shown in FIGS. 15 and 16, it isalso preferable that the displacement-transmitting section 32 is formedin a separated manner as a unit corresponding to each of the pictureelements. In this arrangement, the displacement-transmitting section 32is preferably constructed such that the plate member 32a and thedisplacement-transmitting member 32b are integrated into one unit. Inthese modified embodiments, a color filter 100 and a transparent layer102 are stacked on the displacement-transmitting section 32.

Accordingly, it is possible to allow the displacement-transmittingsection 32 to have slight weight. It is possible to improve the responsespeed of each of the actuator elements 14. Further, it is possible toobtain higher contrast, because this arrangement is scarcely affected bythe operation (displacement) of the surrounding picture elements.

A display Db according to a second modified embodiment is shown in FIG.15, in which the optical waveguide plate 12 and the actuator substrate18 are fixed by means of a crosspiece 104. A black matrix layer 106 isprovided between the forward end of the crosspiece 104 and the opticalwaveguide plate 12. Thus, the black matrix layer 106 is used to adjustthe gap between the transparent layer 102 as the upper layer and theoptical waveguide plate 12. This arrangement is effective in that thegap can be made more uniform for all of the picture elements.

In this modified embodiment, it is preferable for the crosspiece 104 touse a material having a quality which does not cause deformation due toheat and pressure. When the positions of the upper surface of thetransparent layer 102 and the upper surface of the crosspiece 104(surface to make contact with the black matrix layer 106) are aligned,it is advantageous to adjust the gap with ease. The method to realizethis arrangement includes, for example, a method in which a flat glasssurface is used to simultaneously form the transparent layer 102 and thecrosspiece 104, and a method in which the transparent layer 102 and thecrosspiece 104 are formed, followed by polishing to perform figuring.

On the other hand, as shown in FIG. 16, a display Dc according to athird modified embodiment is characterized in that a light-reflectivelayer 108 is formed on the side of the actuator substrate 18 of thedisplacement-transmitting section 32. When the light-reflective layer108 is formed just under the displacement-transmitting section 32 asshown in the drawing, if the light-reflective layer 108 is composed of aconductive layer made of metal or the like, then it is feared that ashort circuit is formed between the pair of electrodes 28a, 28b of theactuator element 14. Therefore, it is desirable that an insulative layer110 is formed between the light-reflective layer 108 and the actuatorelement 14.

Usually, a part of the light 10 is transmitted through thedisplacement-transmitting section 32 in some cases (for example, due thefact that the layer thickness of the displacement-transmitting section32 is thin, or the content of ceramic powder as the material therefor inthe organic resin is low). In such a case, the part of the light 10introduced via the optical waveguide plate 12 is transmitted through thedisplacement-transmitting section 32 to the actuator substrate 18. As aresult, it is feared that the brightness is lowered.

However, as described above, the display Dc according to the thirdmodified embodiment comprises the light-reflective layer 110 which isformed on the side of the actuator substrate 18 of thedisplacement-transmitting section 32. Therefore, the light 10 (indicatedby the optical path “b”), which is transmitted through thedisplacement-transmitting section 32, can be reflected toward theoptical waveguide plate 12. Thus, it is possible to improve thebrightness.

Especially, when the displacement-transmitting section 32 istransmissive with respect to the light 10, and it also has the absorbingproperty for the light 10, then the formation of the light-reflectivelayer 108 is more effective as in the display Dc according to the thirdmodified embodiment in order to improve the brightness, as compared withan arrangement in which the thickness of the displacement-transmittingsection 32 is made thick.

The color layer such as the color filter 100 for constructing thedisplacement-transmitting section 32 is the layer which is used toextract only the light in a specified wavelength region, and itincludes, for example, those which cause light emission by absorbing,transmitting, reflecting, or scattering the light having a specifiedwavelength, and those which convert the incident light into light havinga different wavelength. It is possible to use a transparent member, asemitransparent member, and an opaque member singly or in combination.

The color layer is constructed, for example, as follows. That is, thoseusable for the color layer include, for example, those obtained bydispersing or dissolving a dyestuff or a fluorescent material such asdye, pigment, and ion in rubber, organic resin, light-transmissiveceramic, glass, liquid or the like, those obtained by applying thedyestuff or the fluorescent material on the surface of the foregoingmaterial, those obtained by sintering, for example, the powder of thedyestuff or the fluorescent material as described above, and,thoseobtained by pressing and solidifying the powder of the dyestuff or thefluorescent material. As for the material quality and the structure, thematerial may be used singly, or the materials may be used incombination.

The method for forming the film of the color layer is not specificallylimited, to which it is possible to apply a variety of known filmformation methods. Those usable include, for example, a film laminationmethod in which the color layer in a chip form or in a film form isdirectly stuck on the surface of the optical waveguide plate 12 or theactuator element 14, as well as a method for forming the. color layer inwhich, for example, powder, paste, liquid, gas, or ion to serve as a rawmaterial for the color layer is formed into a film in accordance withthe thick film formation method such as the screen printing, thephotolithography method, the spray dipping, and the application, or inaccordance with the thin film formation method such as the ion beam, thesputtering, the vacuum evaporation, the ion plating, CVD, and theplating.

Alternatively, it is also preferable that a light emissive layer for apart or all of the displacement-transmitting section 32. Those usable asthe light-emissive layer include a fluorescent layer. The fluorescentlayer includes those which are excited by invisible light (ultravioletlight and infrared light) to emit visible light, and those which areexcited by visible light to emit visible light. However, any of them maybe used.

A fluorescent pigment may be also used for the light-emissive layer. Theuse of the fluorescent pigment is effective for those added withfluorescent light having a wavelength approximately coincident with thecolor of the pigment itself, i.e., the reflected light such that thecolor stimulus is large corresponding thereto, and the light emission isvivid. Therefore, the fluorescent pigment is used more preferably toobtain the high brightness for the display element and the display. Ageneral daylight fluorescent pigment is preferably used.

A stimulus fluorescent material, a phosphorescent material, or aluminous pigment is also used for the light-emissive layer. Thesematerials may be either organic or inorganic.

Those preferably used include those formed with the light-emissive layerby using the light-emissive material as described above singly, thoseformed with the light-emissive layer by using the light-emissivematerial as described above dispersed in resin, and those formed Withthe light-emissive layer by using the light-emissive material asdescribed above dissolved in resin.

The afterglow or decay time of the light-emissive material is preferablynot more than 1 second, preferably 30 milliseconds. More preferably theafterglow or decay time is not more than several milliseconds.

When the light-emissive layer is used as a part or all of thedisplacement-transmitting section 32, the light source (not shown) isnot specifically limited provided that it includes the light having awavelength capable of exciting the light-emissive layer and it has anenergy density sufficient for excitation. Those usable include, forexample, cold cathode tube, hot cathode tube, metal halide lamp, xenonlamp, laser including infrared laser, black light, halogen lamp,incandescent lamp, deuterium discharge lamp, fluorescent lamp, mercurylamp, tritium lamp, light emitting diode, and plasma light source.

Next, as shown in FIG. 17, a display Dd according to a fourth modifiedembodiment differs in that a varistor 120 is inserted and connectedbetween the signal line 42 and the column electrode 28b of the actuatorelement 14, the common vertical selection line 40 is connected to apicture element group in one row, and the signal line 42 is formed onthe back surface side of the actuator substrate 18.

As shown in FIG. 18, the vertical selection line 40 is led from the rowelectrode 28a relevant to the picture element of the previous column,and it is connected to the row electrode 28a relevant to the concerningpicture element, giving a form of being wired in series relevant to onerow. The column electrode 28b and the signal line 42 are electricallyconnected to one another via a through-hole 122 formed through thesubstrate 18.

The varistor 120 is a resistor element in which the resistance valuevaries nonlinearly depending on the change in applied voltage. Thevaristor 120 is constructed, for example, by an SiC varistor, a pnpvaristor of Si, or a varistor principally composed of ZnO. The varistor120 has a negative characteristic in which the resistance value isdecreased when the terminal voltage is raised.

FIGS. 19 and 20 show a bending displacement characteristic and anelectric charge-applied voltage characteristic of the actuator elementof the display according to the fourth modified embodiment respectively.The applied voltage, which is indicated along each of the horizontalaxes in FIGS. 19 and 20, is not the voltage directly applied to the pairof electrodes 28a, 28b of the concerning actuator element 14, but itindicates the voltage between the vertical selection line 40 and thesignal line 42.

The operation of the display Dd according to the fourth modifiedembodiment will now be briefly explained. At first, for example, theoperation will be explained, concerning the picture element of the firstrow and first column. When the picture element,is selected, and thevoltage (applied voltage) between the vertical selection line 40 and thesignal line 42 is at the highest level V1, then the varistor 120 is inthe ON state, and the resistance in this state is extremely small (theresistance of the varistor 120 in the ON state is hereinafter referredto as “ON resistance”). Therefore, the time constant, which depends onthe ON resistance and the electrostatic capacity of the varistor 120, isalso small. Thus, the response to the change in applied voltage isquick. Accordingly, the voltage, which is applied to the actuatorelement 14, steeply rises up to a prescribed high voltage (for example,180 V). The amount of electric charge Q steeply increases as well. As aresult, as understood from the bending displacement characteristic shownin FIG. 19, the picture element is in the ON state to cause lightemission, and the amount of electric charge in this state is at themaximum level.

When the concerning picture element is in the unselection state, and thevoltage (applied voltage) between the vertical selection line 40 and thesignal line 42 is at the middle level (V2 to V3), then the varistor 120is in the OFF state, and the resistance in this state is extremely large(the resistance of the varistor 120 in the OFF state is hereinafterreferred to as “OFF resistance”). Therefore, the time constant, whichdepends on the OFF resistance and the electrostatic capacity of thevaristor 120, is also large. Thus, the response to the applied voltageis slow. Accordingly, the voltage, which is applied to the actuatorelement 14, is in the state in which the voltage level (180 V) appliedupon the selection is approximately maintained. Therefore, the amount ofelectric charge Q approximately maintains the maximum level, and thelight emission effected by the picture element is maintained.

When the concerning picture element is reset, and the voltage (appliedvoltage) between the vertical selection line 40 and the signal line 42is at the lowest level V4, then the varistor 120 is in the ON stateagain, and the ON resistance in this state is extremely small.Accordingly, the voltage, which is applied to the actuator element 14,steeply lowers to a prescribed low voltage (for example, −60 V). Asunderstood from the bending displacement characteristic shown in FIG.19, the picture element is in the OFF state, and it is quenched. At thistime, the amount of electric charge Q is at the minimum level.

After that, when the concerning picture element is in the unselectionstate, and the voltage (applied voltage) between the vertical selectionline 40 and the signal line 42 is at the middle level (V2 to V3), thenthe varistor 120 is in the OFF state again, and the resistance in thisstate is extremely large. Therefore, the time constant, which depends onthe OFF resistance and the electrostatic capacity of the varistor 120,is also large. Thus, the response to the applied voltage is slow.Accordingly, the voltage, which is applied to the actuator element 14,is in the state in which the voltage level (−60 V) applied upon thereset is approximately maintained, and hence the light off effected bythe picture element is maintained.

As also understood from the voltage-bending displacement characteristicshown in FIG. 19 and the electric charge-applied voltage characteristicshown in FIG. 20, the display Dd according to the fourth modifiedembodiment exhibits the approximately flat characteristic in which bothof the displacement amount and the amount of electric charge Q arescarcely changed over the range from the high voltage level V1 upon theselection to the middle level (V2 to V3) upon the unselection, and itexhibits the approximately flat characteristic in which both of thedisplacement amount and the amount of the electric charge are scarcelychanged over the range from the low voltage level upon the reset to themiddle level upon the unselection.

In other words, the display Dd according to the fourth modifiedembodiment has the extremely excellent hysteresis characteristic whenthe actuator element 14 is subjected to the operation, providing thememory effect to give the approximately complete shape maintenance.

As described above, in the display Dd according to the fourth modifiedembodiment, the varistor 120 itself has the memory function for theapplied voltage to the actuator element 14. Therefore, a material, whichhas no hysteresis in the bending displacement characteristic as shown inFIG. 21, can be also used as a constitutive material for theshape-retaining layer 26 of the actuator element 14. Thus, it ispossible to widen the range of selection of the material.

In the display Dd according to the fourth modified embodiment, theactuator element 14, the varistor 120, and the vertical selection line40 are formed on the actuator substrate 18, and the signal line 42 isformed on the back surface side of the actuator substrate 18.Alternatively, as shown in FIGS. 22A and 22B, it is also preferable thatthe actuator element 14 and the vertical selection line 40 are formed onthe actuator substrate 18, and the varistor 120 and the signal line 42are formed on the back surface side of the actuator substrate 18.

In this arrangement, as shown in FIG. 23, a varistor substrate 304,which comprises electrodes 300, 302 formed on both surfaces, is preparedin addition to the actuator substrate 18 which comprises a large numberof actuator elements 14 (not shown) formed on the first principalsurface. A large number of through-holes 74 (see FIG. 1), which makecommunication from the first principal surface to the second principalsurface of the actuator substrate 18, are provided corresponding to therespective actuator elements 14. Electrode pads 306 are formed for thethrough-holes 74 on the side of the second principal surface of theactuator substrate 18. That is, the electrodes pads 306 are provided atthe positions corresponding to the actuator elements 14 formed on thefirst principal surface.

On the other hand, as shown in FIG. 23, the varistor substrate 304includes the electrodes 300, 302 which are respectively formed at thepositions corresponding to the respective actuator elements 14 (exactlythe respective electrode pads 306) when the varistor substrate 304 islaminated onto the back surface of the actuator substrate 18. Thevaristor 120 corresponding to each of the actuator elements 14 functionsowing to the electrodes 300, 302 formed on the both surfaces and thesubstrate material existing between the electrodes 300, 302.

The signal line 42 is formed by mutually connecting the electrodes 302,302 formed on the back surface (surface on the side opposite to theactuator substrate 18) of the varistor substrate 304. The electrode 308(for example, the lead electrode for the vertical selection line 40),which requires no varistor function, is electrically connected to theelectrode pad 312 for leading the gate line formed on the secondprincipal surface of the actuator substrate 18 by using, for example,the through-hole 310.

The actuator substrate 18 and the varistor substrate 304 are laminatedwith each other as follows. That is, the second principal surface of theactuator substrate 18 (the surface formed with the large number ofelectrode pads 306) and the first principal surface of the varistorsubstrate 304 are laminated with each other. The electrode pads 306 onthe actuator substrate 18 and the electrodes 300 on the varistorsubstrate 304 are laminated with each other by using, for example,solder or conductive resin. As a result of the lamination, one of theelectrodes (for example, the column electrode 28b) of the actuatorelement 14 is electrically connected to the signal line 42 via thevaristor 120.

The thickness of the varistor substrate 304 is determined by therequired varistor voltage. The electrode area of the varistor 120 isdetermined by the required electrostatic capacity and the requiredcurrent capacity.

For example, the following two methods are conceived as the method forreducing the leak current between the electrodes 300, 300 which aredisposed closely to one another on the first principal surface of thevaristor substrate 304 and between the electrodes 302, 302 which aredisposed closely to one another on the second principal surface of thevaristor substrate 304, and increasing the degree of freedom for thearrangement of the electrodes 300, 302.

(1) Grooves are formed between the closely disposed electrodes 300, 300and between the closely disposed electrodes 302, 302. In thisarrangement, the distances between the electrodes 300, 300 and betweenthe electrodes 302, 302 are substantially increased, and thus thevaristor voltage is increased.

(2) The grain size of the constitutive material for the varistorsubstrate 304 is made fine, and the thickness of the varistor substrate304 is made thin. In this arrangement, the varistor voltage is increasedbetween the closely disposed electrodes 300, 300 and between the closelydisposed electrodes 302, 302 while maintaining the varistor voltagebetween the opposing electrodes 300, 302.

As described above, the varistor substrate 304 for constructing thevaristor 120 is prepared separately from the actuator substrate 18. Thevaristor substrate 304 is laminated onto the actuator substrate 18.Therefore, the wiring structure, which is used to connect the varistor120 between each of the actuator elements 14 and the signal line 42, isextremely simple. The size of the display Dd can be miniaturized.Further, it is extremely advantageous, for example, to improve the yieldof the display Dd and reduce the production cost.

In the display Dd according.to the fourth modified embodiment, the upperelectrode 28a and the lower electrode 28b are formed on the uppersurface and the lower surface of the shape-retaining layer 26respectively. Alternatively, it is also preferable that theshape-retaining layer 26 is directly formed on the vibrating section 22,and the pair of electrodes 28 are formed on the upper surface of theshape-retaining layer 26.

In this arrangement, the pair of electrodes 28a, 28b may have aconfiguration of comb teeth arranged alternately as shown in FIG. 24A.The pair of electrodes 28a, 28b may have a spiral configuration in whichthey are arranged in parallel to one another and separated from eachother as shown in FIG. 24B. Alternatively, the pair of electrodes 28a,28b may have a branched configuration in the same manner as in thearrangement shown in FIG. 14. Also in this case, the varistor 120 may beformed either on the principal surface or on the back surface of theactuator substrate 18 (see FIG. 1) in the same manner as in the displayDd according to the fourth modified embodiment. In the arrangement alongwith FIG. 14, the varistor (not shown) is formed on the back surface ofthe actuator substrate 18, and one of the electrodes 28a is electricallyconnected to the varistor via the mediating conductor 78 and thethrough-hole 74.

Next, a display De according to a fifth modified embodiment will beexplained with reference to FIGS. 25 to 28. Components or partscorresponding to those of the display D according to the embodiment ofthe present invention are designated by the same reference numerals,duplicate explanation of which will be omitted.

As shown in FIG. 25, the display De according to the fifth modifiedembodiment is basically constructed in approximately the same manner asthe display D according to the embodiment of the present invention.However, the former is different from the latter in that a piezoelectricrelay 400 is inserted and connected between the upper electrode 28a ofthe actuator element 14 and the ground line 76. The display De accordingto the fifth modified embodiment is structurally different from thedisplay D according to the embodiment of the present invention as well,because of those relevant to the provision of the piezoelectric relay400.

The display De according to the fifth modified embodiment will bespecifically explained. As shown in FIGS. 26 and 27, the display Deaccording to the fifth modified embodiment comprises the piezoelectricrelays 400 which are arranged at positions adjacent to the respectiveactuator elements 14 of the actuator substrate 18 respectively. A hollowspace 402 for constructing the piezoelectric relay 400 is provided atthe inside of the actuator substrate 18 in addition to the hollow space20 for constructing the actuator element 14. The hollow space 402 alsocommunicates with the outside via a through-hole (not shown) having asmall diameter provided on the back surface side of the actuatorsubstrate 18.

Therefore, also in this arrangement, the portion of the actuatorsubstrate 18, at which the hollow space 402 is formed, is thin-walled.The other portion of the actuator substrate 18 is thick-walled. Thethin-walled portion has a structure which tends to undergo vibration inresponse to external stress, and it functions as a vibrating section 404for the piezoelectric relay. The portion other than the hollow space 402is thick-walled, and it functions as a fixed section 406 for thepiezoelectric relay for supporting the vibrating section 404.

As shown in the drawing, each of the piezoelectric relays 400 comprisesthe vibrating section 404 and the fixed section 406 described above; aswell as a main relay body 414 including a shape-retaining layer 408composed of, for example, a piezoelectric/electrostrictive layer or ananti-ferroelectric layer formed on the vibrating section 404, a lowerelectrode 28b formed on the lower surface of the shape-retaining layer408, an intermediate electrode 410 (electrode connected to the verticalselection line 40) formed on the upper surface of the shape-retaininglayer 408, an insulative layer 412 formed on the intermediate electrode410, and an upper electrode 28a formed on the insulative layer 412; ablack matrix layer 416 provided at a position corresponding to each ofthe piezoelectric relays 400 on the surface of the optical waveguideplate 12 on the side of the driving section; and a ground electrode 418formed on the surface of the black matrix layer 416 opposing to thepiezoelectric relay 400. It is preferable to use a metal film composedof, for example, Cr, Al, Ni, or Ag as the black matrix layer 416,because of the following reason. That is, the metal film absorbs lesslight, and hence it is possible to suppress the attenuation and thescattering of the light transmitted through the optical waveguide plate12. In order to improve the contrast, a film containing carbon black,black pigment, or black dye is also preferably used. This modifiedembodiment is illustrative of the case in which the black matrix layer416 is formed. Alternatively, a transparent electrode is used as theground electrode 418 in some cases without forming the black matrixlayer 416.

Of the several electrodes described above, the lower electrode 28b iscommon to the lower electrode (electrode connected to the signal line42) 28b of the actuator element 14. The upper electrode 28a is common tothe upper electrode 28a of the actuator element 14.

In the display De according to the fifth modified embodiment, forexample, a selection signal (for example a positive high level electricpotential) is applied to one vertical selection line 40, and thus theconcerning vertical selection line 40 is selected.

Also in the display De according to the fifth modified embodiment, thesupply of the data signal to the unselected row can be avoided in thesame manner as in the display D according to the embodiment of thepresent invention. It is unnecessary to operate the picture element(actuator element) 14 concerning the unselected row. It is possible toeffectively reduce the electric power consumption. The light emissioncan be effected for the picture element during the unselection periodTu. Therefore, it is possible to realize the high brightness. Further,it is unnecessary to form any large wiring pattern on the actuatorsubstrate 18. Thus, it is possible to simplify the wiring arrangement.

In the display De according to the fifth modified embodiment, theactuator element 14, the piezoelectric relay 400, and the groundelectrode 418 are formed on the actuator substrate 18. Alternatively, asshown in FIG. 28, it is also preferable that the actuator element 14 isformed on the actuator substrate 18, and the piezoelectric relay 400 andthe ground electrode 418 are formed on the back surface side of theactuator substrate 18.

As shown in FIG. 28, for example, this arrangement can be achieved suchthat the hollow space 402 for constructing the piezoelectric relay 400is provided under the hollow space 20 for constructing the actuatorelement 14 in the actuator substrate 18, and the main relay body 414 isformed under the hollow space 402.

In this arrangement, it is impossible to commonly use the signal line42. Therefore, the following structure may be used. That is, a verticalselection line 420, which is exclusively used for switching, is newlyprovided and wired on the back surface side of the actuator substrate18. Further, the upper electrode 28a, which is formed on thepiezoelectric relay 400, is wired from the actuator element 14 via athrough-hole 422 provided through the actuator substrate 18. The groundelectrode 418, which is selectively contacted with the upper electrode28a, is formed on a printed circuit board 424 disposed under theactuator substrate 18.

The electrodes 28a, 28b may be formed on the shape-retaining layer 26,and they may be formed as the pair of electrodes having a comb-teethshaped configuration, a spiral configuration, or a branchedconfiguration, in the same manner as in the display D according to theembodiment of the present invention and the displays Da to Dd accordingto the first to fourth modified embodiments.

Explanation of Gradation Control Based on Temporal Modulation System

The gradation control based on the temporal modulation system will nowbe explained with reference to FIGS. 29 to 41. At first, as shown inFIG. 29, it is assumed that the display period for one image is definedto be one field, and one divided period, which is obtained by equallydividing the one field into a plurality of ones, is defined to be asubfield. The display cycle Td is set for each of the subfields. Forexample, the maximum gradation level is 8 when the one field is equallydivided into seven.

The row electrode-driving circuit 202 is subjected to the timing controlby the signal control circuit so that all row selection is completedwithin each subfield. Therefore, the time (selection period) forselecting one row by the row electrode-driving circuit 202 is regulatedby the time width obtained by dividing the time width of the subfield bythe number of rows of the driving section 16, for which the time widthor a time width shorter than the time width described above is selected.Preferably, 1/m of the time width (m is an arbitrary real number from 1to 5, preferably a real number from 1 to 3) is selected.

The driving device 200 according to the embodiment of the presentinvention is controlled so that the signal control circuit 206 is usedto determine, in the one field, the light emission start timing and thelight emission maintenance period having a variable length irrelevant tothe selection/unselection state of the concerning picture element,depending on the gradation level of the selected picture element.

Specified embodiments of the gradation control according to theembodiment of the present invention will be explained below withreference to FIGS. 30A to 41. In order to avoid any complicated drawing,the embodiments shown in FIGS. 30A to 41 are illustrative of thesimplified format in which one field is divided into seven subfields SF1to SF7, and the number of rows is 4.

First Specified Embodiment

As shown in FIG. 30A, the first specified embodiment resides in a systemin which one selection period S and display cycles Td of a numbercorresponding to the maximum gradation level are allotted in one field.In this embodiment, the display cycle Td is composed of the unselectionperiod U and the reset period R.

Basically, the unselection period U is used to select all of the rowsother than the row relevant to the concerning picture element by the aidof the row electrode-driving circuit 202, and it is designed to satisfy“unselection period U≧selection period S×(number of rows−1)”. The resetperiod R is used to select the row relevant to the concerning pictureelement in the same manner as in the selection period S, for which anapproximately equivalent period is set.

Further, as shown in FIG. 30B, the selection pulse Ps is outputtedduring the selection period S by the aid of the row electrode-drivingcircuit 202, the unselection signal Su is outputted during theunselection period U In the display cycle Td, and the reset pulse Pr isoutputted during the reset period R.

The signal control circuit 206 makes control for the columnelectrode-driving circuit 204 as follows. That is, the control is madesuch that the ON signal is outputted during the light emissionmaintenance period, and the OFF signal is outputted at least at the endtiming of the light emission maintenance period during the period otherthan the light emission maintenance period.

For example, in relation to the picture element of the first row andfirst column, if the gradation level of the concerning picture elementis, for example, 5, the control is performed as follows. That is, the ONsignal is outputted in synchronization with the selection period S andthe respective reset periods R from the first display cycle Td1 to thefourth display cycle Td4. and the OFF signal is outputted insynchronization with at least the reset period R in the fifth displaycycle Td5 which firstly indicates the end of the light emissionmaintenance period, of the respective reset periods R from the fifthdisplay cycle Td5 to the seventh display cycle Td7. The signal, which isoutputted during the respective reset periods R in the residual sixthand seventh display cycles Td6 and Td7, may be either the ON signal orthe OFF signal. The first specified embodiment is illustrative of thecase in which the OFF signal is outputted.

Similarly, as shown in FIG. 30C, in relation to the picture element ofthe second row, and first column, if the gradation level of theconcerning picture element is, for example, 3, the control is performedas follows. That is, the ON signal is outputted in synchronization withthe selection period S and the respective reset periods R in the firstand second display cycles Td1 and Td2, and the OFF signal is outputtedin synchronization with at least the reset period R in the third displaycycle Td3 which firstly indicates the end of the light emissionmaintenance period, of the respective reset periods R from the thirddisplay cycle Td3 to the seventh display cycle Td7. The signal, which isoutputted during the respective reset periods R in the residual fourthto seventh display cycles Td4 to Td7, may be either the ON signal or theOFF signal. This embodiment is illustrative of the case in which the OFFsignal is outputted.

Consideration will be specifically made in relation to the change involtage. At first,,as shown in FIG. 30B, in relation to the pictureelement of the first row and first column, the selection pulse Ps havingthe peak voltage of −100 V is outputted during the selection period S.At this time, the ON signal having the peak voltage of 80 V is suppliedto the signal line 42. Therefore, the actuator element 14 is appliedwith 80−(−100) V=180 V. According to the bending displacementcharacteristic shown in FIG. 7, the actuator element 14 makes thedisplacement up to Point E in the first direction. That is, theconcerning picture element is in the light emission state.

Thereafter, the unselection signal Su having the peak voltage of −20 Vis outputted during the unselection period U in the first display cycleTd1. During this period, the row electrode-driving circuit 202 is usedto select the second row and the followings, and the ON signal or theOFF signal is randomly supplied to the signal line 42 of the firstcolumn. In other words, the actuator element 14 of the first row andfirst column is applied with 80−(−20) V=100 V or 0−(−20) V=20 V.

Therefore, as also understood from the bending displacementcharacteristic shown in FIG. 7, the concerning actuator element 14undergoes the bending displacement of Point F or Point G. The actuatorelement 14 approximately maintains the original displacement state. Thatis, the light emission state of the concerning picture element ismaintained.

The reset pulse Pr having the peak voltage of 60 V is outputted duringthe reset period R in the first display cycle Td1. At this time, the ONsignal is supplied to the signal line of the first column. Therefore,the actuator element 14 is applied with 80−60 V=20 V. Thus, the lightemission state of the concerning picture element is maintained.

The operation in the first display cycle Td1 is performed until theunselection period U in the fifth display cycle Td5 in the same manneras described above.

The OFF signal is supplied to the first column during the reset period Rand the followings,in the next fifth display cycle Td5. Accordingly, thereset pulse Pr having the peak voltage of 60 V is outputted during thereset period R in the fifth display cycle Td5. At this time, the OFFsignal having the peak voltage of 0 V is supplied to the signal line 42.Therefore, the concerning actuator element 14 is applied with 0−60 V=−60V. According to the bending displacement characteristic shown in FIG. 7,the actuator element 14 is restored (reset) to Point A. Thus, theconcerning picture element is in the light off state.

Thereafter, the unselection signal having the peak voltage of −20 V isoutputted during the unselection period U in the sixth display cycleTd6. In this period, the row electrode-driving circuit 202 is used toselect the second row and the followings. The ON signal or the OFFsignal is randomly supplied to the signal line of the first column. Theactuator element 14 of the first row and first column is applied with80−(−20) V=100 V or 0−(−20) V=20 V.

Therefore, as also understood from the bending displacementcharacteristic shown in FIG. 7, the concerning actuator element 14 is inthe displacement state of the Point C or Point D. Thus, the light offstate of the concerning picture element is maintained.

The reset pulse Pr having the peak voltage of 60 V is outputted duringthe reset period R in the sixth display cycle Td6. At this time, the OFFsignal is supplied to the signal line 42 of the first column. Therefore,the actuator element 14 is supplied with 0−60 V=−60 V. Thus, the lightoff state of the concerning picture element is maintained. The operationin the sixth display cycle Td6 is also performed in the seventh displaycycle Td7 in the same manner as described above.

As described above, in relation to the picture element of the first rowand first column having the gradation level of 5, the light emissionstate ranges from the head of the one field to the start point of timeof the reset period R in the fifth display cycle Td5, and the light offstate ranges from the start point of time of the reset period R in thefifth display cycle Td5 to the terminal end of the one field.

Similarly, as shown in FIG. 30C, in relation to the picture element ofthe second row and first column having the gradation level of 3, thelight emission state ranges from the head of the one field to the startpoint of time of the reset period R in the third display cycle Td3, andthe light off state ranges from the start point of time of the resetperiod R in the third display cycle Td3 to the terminal end of the onefield.

According to the first specified embodiment, as shown in FIG. 30A, thefollowing operation is effected assuming that the selection period S isallotted to the head of the one field. That is, one display cycle Td isselected, or a plurality of display cycles Td are continuously selectedfrom the head of the one field, depending on the gradation level of theconcerning picture element. The ON signal is outputted insynchronization with the head selection period S and the reset period inthe selected display cycle Td. The OFF signal is outputted insynchronization with the respective reset periods R in the residualdisplay cycles Td.

In this embodiment, only one cycle of light emission and light off isprovided for the concerning picture element in the one field. Thus, itis possible to effectively reduce the electric power consumption ascompared with the driving system (adopted, for example, in the plasmadisplay) in which one field is divided into a plurality of subfields,and the forcible reset operation is performed for each of the subfields.

An illustrative experiment will now be described. In this illustrativeexperiment, the display D according to the embodiment of the presentinvention was used to measure the voltage waveform applied to theactuator element 14 obtained when the driving system according to thefirst specified embodiment was used or when Comparative Example (generaldriving system used in the plasma display) was used, while the change inlight intensity (Ld) scattered from the concerning picture element wasmeasured by using a photodiode. A measurement result obtained by usingthe first specified embodiment is shown in FIG. 31, and a measurementresult obtained by using Comparative Example is shown in FIG. 32.

As for the first specified embodiment, the following fact is appreciatedas shown in FIG. 31. That is, the high level pulse-shaped voltage V_(H)is applied to the actuator element 14 on the basis of the output of theselection pulse Ps during the output period of the ON signal. Thevoltage waveform of 20 V and the voltage waveform of 100 V are appliedrandomly in the following display cycles. The low level pulse-shapedvoltage V_(L) is applied to the actuator element 14 on the basis of theoutput of the reset pulse Pr during the output period of the OFF signal.

According to this fact, as also understood from the electriccharge-applied voltage characteristic shown in FIG. 8, the electricpower, which corresponds to the area surrounded by “-x-”, is consumedonly once in the one field in the case of the first specifiedembodiment. This fact is also true for the displays Da to De accordingto the first to fifth modified embodiments. Especially, in the case ofthe display Dd according to the fourth modified embodiment based on theuse of the varistor 120, the electric power, which corresponds to thearea surrounded by “-x-” in the electric charge-applied voltagecharacteristic shown in FIG. 20, is consumed only once in the one field.

On the other hand, as for Comparative Example, as shown in FIG. 32, theapplied voltage changes from the high level V_(H) (180 V) to the lowlevel V_(L) (−60 V) is one display cycle Td. Therefore, as alsounderstood from the electric charge-applied voltage characteristic shownin FIG. 8, the electric power, which corresponds to the area surroundedby “-x-”, is consumed in one display cycle Td. In other words, theelectric power, which corresponds to the area surrounded by “-x-”, isconsumed in the amount corresponding to the number of times of thedisplay cycles Td in the one field. It is understood that the electricpower consumption is increased as compared with the first specifiedembodiment.

As described above, when the first specified embodiment is adopted, itis possible to effectively reduce the electric power consumption of thepanel type display.

Further, in the first specified embodiment, the light emission state ismaintained over the display cycles selected depending on the gradationlevel of the concerning picture element. Therefore, it is also possibleto realize the improvement in brightness. Furthermore, good linearity isobtained between the gradation and the brightness, making it possible toperform highly accurate gradational expression. Moreover, the efficiencyof the light emission time is also improved. Especially, the displayaccording to the fourth modified embodiment has the good hysteresischaracteristic concerning the voltage-displacement characteristic.Therefore, it is possible to sufficiently maintain the brightness oflight emission, and it is possible to realize the high brightness of thedisplayed image.

Second Specified Embodiment

Next, a gradation control system according to the second specifiedembodiment will be explained with reference to FIGS. 33A to 33C. Asshown in FIG. 33A, the second specified embodiment resides inapproximately the same gradation control system as that used in thefirst specified embodiment described above (see FIG. 30A). However, theformer is different from the latter in that the display cycles Td1 toTd7 of a number corresponding to the maximum gradation level and onereset period R are allotted in the one field, and each of the displaycycles Td1 to Td7 is composed of the selection period S and theunselection period U.

The signal control circuit 206 makes control for the columnelectrode-driving circuit 204 as follows. That is, the control is madesuch that the OFF signal is outputted during the periods other than thelight emission maintenance period, and the ON signal is outputted atleast at the light emission start timing during the light emissionmaintenance period.

For example, as shown in FIG. 33B, in relation to the picture element ofthe first row and first column, if the gradation level of the concerningpicture element is, for example, 5, the control is performed as follows.That is, the OFF signal is outputted in synchronization with therespective selection periods S in the first and second display cycles.The ON signal is outputted in synchronization with at least theselection period S in the third display cycle Td3 which firstlyindicates the light emission start timing, of the respective selectionperiods S from the third display cycle Td3 to the seventh display cycleTd7. The OFF signal is outputted in synchronization with the terminalend reset period R in the one field. The signal, which is outputtedduring the respective selection periods S in the fourth to seventhdisplay cycles Td4 to Td7 in the light emission maintenance period, maybe either the ON signal or the OFF signal. The second specifiedembodiment is illustrative of the case in which the ON signal isoutputted.

Similarly, as shown in FIG. 33C, in relation to the picture element ofsecond row and first column, if the gradation level of the concerningpicture element is, for example, 3, the control is performed as follows.That is, the OFF signal is outputted in synchronization with therespective selection periods S from the first display cycle Td1 to thefourth display cycle Td4. The ON signal is outputted in synchronizationwith at least the selection period S in the fifth display cycle Td5which firstly indicates the light emission start timing, of therespective selection periods S from the fifth display cycle Td5 to theseventh display cycle Td7. The OFF signal is outputted insynchronization with the terminal end reset period R in the one field.The signal, which is outputted during the respective selection periods Sin the sixth and seventh display cycles Td6 and Td7 in the lightemission maintenance period, may be either the ON signal or the OFFsignal. The second specified embodiment is illustrative of the case inwhich the ON signal is outputted.

Consideration will be specifically made in relation to the change involtage. At first, as shown in FIG. 33B, in relation to the firstdisplay cycle Td1 of the picture element of the first row and firstcolumn, the selection pulse Ps of (peak voltage −100 V) is outputtedduring the selection period S. At this time, the OFF signal having thepeak voltage of 0 V is supplied to the signal line 42.

Therefore, the actuator element 14 is applied with 0−(−100) V=100 V. Thebending displacement of the actuator element 14 has been reset andrestored in the previous field. Therefore, the displacement state ofPoint D is given according to the bending displacement characteristicshown in FIG. 7. Thus, the light off state of the concerning pictureelement is maintained.

The unselection signal Su having the peak voltage of −20 V is outputtedduring the unselection period U in the first display cycle Td1. In thisperiod, the row electrode-driving circuit 202 is used to select thesecond row and the followings. The ON signal or the OFF signal israndomly supplied to the signal line 42 of the first column. Theactuator element 14 of the first row and first column is applied with80−(−20) V=100 V or 0−(—20) V=20 V.

Therefore, as also understood from the bending displacementcharacteristic shown in FIG. 7, the concerning actuator element 14 is inthe displacement state of Point C or Point D. Thus, the light off stateof the concerning picture element is maintained.

The operation in the first display cycle Td1 is also performed in thesecond display cycle Td2 in the same manner as described above. The ONsignal is supplied to the first column in the selection period S in thenext third display cycle Td3 and the followings. Accordingly, theselection pulse Ps having the peak voltage of −100 V is outputted duringthe selection period S in the third display cycle Td3. At this time, theON signal having the peak voltage of 80 V is supplied to the signal line42. Therefore, the concerning actuator element 14 is applied with80−(−100) V=180 V. According to the bending displacement characteristicshown in FIG. 7, the actuator element 14 makes bending displacement upto Point E. Thus, the concerning picture element is in the lightemission state.

Thereafter, the unselection signal Su having the peak voltage of −20 Vis outputted during the unselection period U in the third display cycleTd3. The ON signal or the OFF signal is randomly supplied to the signalline 42 of the first column during this period. The applied voltage Vpto the concerning actuator element 14 is 100 V or 20 V. As alsounderstood from the bending displacement characteristic shown in FIG. 7,the bending displacement of Point F or Point G is given. In this state,the original displacement state of the actuator element 14 isapproximately maintained. The light emission state of the concerningpicture element is maintained.

The operation in the third display cycle Td3 is performed in the samemanner as described above from the fourth display cycle Td4 to theseventh display cycle Td7.

The OFF signal is supplied to the first column in the terminal end resetperiod R. Accordingly, the concerning actuator element 14 is appliedwith 0−60 V=−60 V. According to the bending displacement characteristicshown in FIG. 7, the actuator element 14 is restored (reset) to Point A,and the concerning picture element is in the light off state.

As described above, the picture element of the first row first columnhaving the gradation level of 5 is operated as follows as shown in FIG.33B. That is, the light off state is given from the head of the onefield to the second display cycle Td2. The light emission state is givenfrom the third display cycle Td3 to the seventh display cycle Td7. Thelight off state is given in the terminal end reset period R.

Similarly, as shown in FIG. 33C, in relation to the picture element ofthe second row first column having the gradation level of 3, the lightoff state is given from the head of the one field to the fourth displaycycle Td4, the light emission state is given from the fifth displaycycle Td5 to the seventh display cycle Td7, and the light off state isgiven in the terminal end reset period R.

According to the second specified embodiment, as shown in FIG. 33A, thefollowing operation is effected assuming that the reset period R isallotted to the rear end of the one field. That is, one display cycle Tdis selected, or a plurality of display cycles Td are continuouslyselected from the rear end of the one field, depending on the gradationlevel of the concerning picture element. The ON signal is outputted insynchronization with the respective selection periods S in the selecteddisplay cycles Td. The OFF signal is outputted in synchronization withthe rear end reset period R.

Also in this embodiment, only one cycle of light emission and light offis provided for the concerning picture element in the one field. Thus,it is possible to effectively reduce the electric power consumption. Thelinearity between the gradation and the brightness is excellent, and itis possible to make highly accurate gradational expression. Further, theefficiency of the light emission time is also enhanced. Especially,owing to the selection period which exists. in each of the selecteddisplay cycles, the brightness can be sufficiently maintained over thelight emission maintenance period for the concerning picture element.

Third Specified Embodiment

Next, a gradation control system according to the third specifiedembodiment will be explained with reference to FIG. 34. As shown in FIG.34, the third specified embodiment resides in approximately the samegradation control system as that used in the second specified embodimentdescribed above (see FIG. 33A). However, in this specified embodiment,the maximum gradation level to be handled is lowered to prolong thetemporal length of the unselection period U in each of the displaycycles Td. In this specified embodiment, the temporal length of theselection period S may be not more than the temporal length of theselection period S in the second specified embodiment.

According to the third specified embodiment, the ratio of the lightemission maintenance period for the picture element is increased.Therefore, it is possible to realize the higher brightness.

Fourth Specified Embodiment

Next, a gradation control system according to the fourth specifiedembodiment will be explained with reference to FIGS. 35A to 35C. Asshown in FIG. 35A, the fourth specified embodiment resides inapproximately the same gradation control system as that used in thefirst specified embodiment described above (see FIG. 30A). However, theformer is different from the latter in that the odd/even-adjusting cycleTc including the unit unselection period U(1) having the predeterminedlength between the two selection periods S and the display cycles Td1 toTd3 of a number corresponding to the maximum gradation level areallotted in the one field, and the redundant unselection period U(2)having the length twice the predetermined length and the reset period Rare set in each of the display cycles Td1 to Td3.

The signal control circuit 206 makes control for the columnelectrode-driving circuit 204 as follows. That is, the control is madesuch that the ON signal is outputted in any of the selection periods Sincluded in the odd/even-adjusting cycle, and the OFF signal isoutputted at the end timing of the light emission maintenance period.

For example, as shown in FIG. 35B, in relation to the picture element ofthe first row and first column, when the gradation level of the pictureelement is, for example, an odd number of 5, the control is performed asfollows. That is, the ON signal is outputted in,synchronization with thehead selection period S in the odd/even-adjusting cycle Tc whichindicates the start of the light emission maintenance period. The OFFsignal is outputted in synchronization with the reset period R in thesecond display cycle Td2 which indicates the end of the light emissionmaintenance period. The signal, which is outputted during the otherselection period and the reset periods, maybe either the ON signal orthe OFF signal. The fourth specified embodiment is illustrative of thecase in which the ON signal is outputted during the rear end selectionperiod S in the odd/even-adjusting cycle Tc included in the lightemission maintenance period and the reset period R in the first displaycycle Td1, and the OFF signal is outputted during the reset period R inthe third display cycle Td3 included in the period other than the lightemission maintenance period.

Accordingly, the picture element of the first row and first column is inthe light emission state from the head of the one field to the point oftime of start of the reset period R in the second display cycle Td2, andit is in the light off state from the point of time of end of the resetperiod R in the second display cycle Td2 to the terminal end of the onefield.

For example, as shown in FIG. 35C, in relation to the picture element ofthe second row and first column, when the gradation level of the pictureelement is, for example, an even number of 6, the control is performedas follows. That is, the ON signal is outputted in synchronization withthe rear end selection period S in the odd/even-adjusting cycle Tc whichindicates the start of the light emission maintenance period. The OFFsignal is outputted in synchronization with the reset period R in thethird display cycle Td3 which indicates the end of the light emissionmaintenance period. The signal, which is outputted during the otherselection period S and the reset periods R, may be either the ON signalor the OFF signal. The fourth specified embodiment is illustrative ofthe case in which the ON signal is outputted during the respective resetperiods R in the first and second display cycles Td1 and Td2 included inthe light emission maintenance period, and the OFF signal is outputtedduring the head selection period S of the odd/even-adjusting cycle Tcincluded in the period other than the light emission maintenance period.

Accordingly, the picture element of the second row and first column isin the light off state from the head of the one field to the terminalend of the unit unselection period U(1) of the odd/even-adjusting cycleTc, it is in the light emission state from the selection period S at therear end of the odd/even-adjusting cycle Tc to the point of time ofstart of the reset period R in the third display cycle Td3, and it is inthe light off state during the reset period R in the third display cycleTd3.

According to the fourth specified embodiment, the following operation iseffected, for example, assuming that the eight gradations are expressedwith the one field. In general, if the field is constructed by only unitdisplay cycles, it is necessary to perform the selective scanning eighttimes for one row. However, when the allotment is made with the displaycycle designed with the redundant unselection period U(2) having thelength twice the predetermined length, it is enough to perform theselective scanning five times for one row. Thus, it is possible toreduce the cycle (row scanning cycle) for selecting one row. Thisreduces the number of times of electric power consumption correspondingto the area surrounded by “-▴-” depicted in the electric charge-appliedvoltage characteristic shown in FIG. 8. This results in the reduction ofthe electric power consumption. Further, this also results in the highbrightness of the selected picture element, because the light emissionstate is maintained in the redundant unselection period U(2).

In view of the reduction of the number of times of electric powerconsumption corresponding to the area surrounded by “-▴-” depicted inthe electric charge-applied voltage characteristic, a sufficient effectcan be exhibited by making application to the display which does nothave good hysteresis characteristic, such as the display Dd according tothe fourth modified embodiment. Of course, even when application is madeto the display Dd according to the fourth modified embodiment, it isextremely advantageous to reduce the frequency for the row selection.

Fifth Specified Embodiment

Next, a gradation control system according to the fifth specifiedembodiment will be explained with reference to FIGS. 36A to 36C. Asshown in FIG. 36A, the fifth specified embodiment resides inapproximately the same gradation control system as that used in thefourth specified embodiment described above (see FIG. 35A). However, theformer is different from the latter in that the display cycles Td1 toTd3 of a number corresponding to the maximum gradation level and theodd/even-adjusting cycle Tc including the unit unselection period U(1)having the predetermined length between the two reset periods R areallotted in the one field, and the redundant unselection period U(2)having the length twice the predetermined length is set in each of thedisplay cycles Td1 to Td3.

The signal control circuit 206 makes control for the columnelectrode-driving circuit 204 as follows. That is, the control is madesuch that the ON signal is outputted at the start timing of the lightemission maintenance period, and the OFF signal is outputted in any ofthe reset periods R included in the odd/even-adjusting cycle.

For example, as shown in FIG. 36B, in relation to the picture element ofthe first row and first column, when the gradation level of the pictureelement is, for example, an odd number of 5, the control is performed asfollows. That is, the ON signal is outputted in synchronization with theselection period S in the second display cycle Td which indicates thestart of the light emission maintenance period. The OFF signal isoutputted in synchronization with the reset period R at the rear end ofthe odd/even-adjusting cycle Tc which indicates the end of the lightemission maintenance period. The signal, which is outputted during theother selection periods S and the reset period R, may be either the ONsignal or the OFF signal. The fifth specified embodiment is illustrativeof the case in which the ON signal is outputted during the selectionperiod S in the third display cycle Td3 included in the light emissionmaintenance period and the reset period R at the head of theodd/even-adjusting cycle Tc, and the OFF signal is outputted during theselection period S in the first display cycle Td1 included in the periodother than the light emission maintenance period.

Accordingly, the picture element of the first row and first column is inthe light off state from the head of the one field to the first displaycycle Td1, it is in the light emission state from the second displaycycle Td2 to the point of time of start of the rear end reset period Rin the odd/even-adjusting cycle Tc, and it is in the light off state inthe terminal end reset period R.

As shown in FIG. 36C, for example, in relation to the picture element ofthe second row and first column, when the gradation level of the pictureelement is, for example, an even number of 6, the control is performedas follows. That is, the ON signal is outputted in synchronization withthe selection period S in the first display cycle Td1 which indicatesthe start of the light emission maintenance period. The OFF signal isoutputted in synchronization with the head reset period R in theodd/even-adjusting cycle Tc which indicates the end of the lightemission maintenance period. The signal, which is outputted during theother selection periods S and the reset period R, may be either the ONsignal or the OFF signal. The fifth specified embodiment is illustrativeof the case in which the ON signal is outputted during the respectiveselection periods S in the second and third display cycles Td2 and Td3included in the light emission maintenance period, and the OFF signal isoutputted during the rear end reset period R of the odd/even-adjustingcycle Tc included in the period other than the light emissionmaintenance period.

Accordingly, the picture element of the second row and first column isin the light emission state from the head of the one field to the thirddisplay cycle Td3, and it is in the light off state from theodd/even-adjusting cycle Tc to the terminal end of the one field.

Also in the fifth specified embodiment, it is possible to reduce the rowscanning cycle. Further, it is possible to reduce the electric powerconsumption and realize the high brightness.

The first to third specified embodiments described above areillustrative of the case in which the equally spaced display cycles Td,which are of the number corresponding to the maximum gradation level,are allotted in the one field. Alternatively, as in the sixth andseventh specified embodiments described below, the following arrangementis also preferred. That is, at least one unit display cycle includingthe unit unselection period having the predetermined length and at leastone redundant display cycle are allotted in the one field. The redundantdisplay cycle is provided with the redundant unselection period havingthe length which is n-times the predetermined length (n is an integer ofnot less than 2). In this description, n is conveniently defined as“degree of redundancy”.

The following expressions are satisfied:Z=(quotient of X/n)−1Y=X−Z×n[total number of subfields (Y+Z)=(X/n−1)+n]provided that the maximum gradation level is X, the number of unitdisplay cycles is Y, and the number of redundant display cycles is Z.Further, “a” individuals of selection periods S are allotted to therespective display cycles from the head of the one field, and “b”individuals of reset periods R are allotted to the respective displaycycles from the rear end of the one field. On this assumption, there isgiven:a+b=Y+Z+1.In the case of b=n, all of the gradations included in the maximumgradation level can be expressed. However, on the assumption of b=n−1,one or several gradation levels may be curtailed. This reduces the rowscanning cycles, and hence it is possible to realize the low electricpower consumption.

Specified embodiments based on this gradation control system will beexplained below with reference to FIGS. 37 to 39.

Sixth Specified Embodiment

In the sixth specified embodiment, the degree of redundancy n is 4, andthe maximum gradation level X is 16 as shown in FIG. 37. In this case,the number Z of the redundant display cycles TD is (quotient of16/4)−1=3, and the number Y of the unit display cycles Td is 16−3×4=4.

In the sixth specified embodiment, three redundant display cycles TD1 toTD3 are continuously allotted from the head of the one field, and thenfour unit display cycles Td1 to Td4 are continuously allotted. Further,four selection periods S are allotted to the respective display cyclesfrom the head of the one field. Four reset periods R are allotted to therespective display cycles from the rear end of the one field.

In the sixth specified embodiment, when the gradation levels 1 to 4 areexpressed, then the ON signal is outputted in synchronization with thefourth selection period S allotted to the former stage of the first unitdisplay cycle Td1, and the ON signal and the OFF signal are outputted insynchronization with the reset periods in the unit display cycles Td1 toTd4 of the number corresponding to the gradation level of the concerningpicture element.

When the gradation levels 5 to 8 are expressed, then the ON signal isoutputted in synchronization with the third selection period S allottedto the former stage of the third redundant display cycle TD3 and thefourth selection period is S described above, and the ON signal and theOFF signal are outputted in synchronization with the reset periods inthe unit display cycles Td1 to Td4 of the number corresponding to thegradation level of the concerning picture element.

When the gradation levels 9 to 12 are expressed, then the ON signal isoutputted in synchronization with the second selection period S allottedto the former stage of the second redundant display cycle TD2 and thethird and fourth selection periods S described above, and the ON signaland the OFF signal are outputted in synchronization with the resetperiods R in the unit display cycles Td1 to Td4 of the numbercorresponding to the gradation level of the concerning picture element.

When the gradation levels 13 to 16 are expressed, then the ON signal isoutputted in synchronization with the head selection period S to thefourth selection period S, and the ON signal and the OFF signal areoutputted in synchronization with the reset periods R in the unitdisplay cycles Td1 to Td4 of the number corresponding to the gradationlevel of the concerning picture element.

According to the sixth specified embodiment, for example, when it isassumed that the sixteen gradations are expressed in the one field, itis enough to perform the selective scanning eight times for one row.Thus, it is possible to greatly reduce the row scanning cycles. As aresult, it is possible to realize the reduction of electric powerconsumption and the high brightness.

Seventh Specified Embodiment

The seventh embodiment is constructed in approximately the same manneras the sixth embodiment as shown in FIG. 38. However, the former isdifferent from the latter in that four unit display cycles Td1 to Td4are continuously allotted from the head of the one field, and then threeredundant display cycles TD1 to TD3 are continuously allotted.

In the seventh specified embodiment, when the gradation levels 1 to 4are expressed, the OFF signal is outputted in synchronization with therespective reset periods, and the start timing of the ON signal iscontrolled so that the number of the unit display cycles Td1 to Td4 isincreased or decreased depending on the gradation level. When thegradation levels 5 to 8 are expressed, the OFF signal is outputted insynchronization with the respective reset periods R allotted to the rearend of the first redundant display cycle TD1 and the followings, and thestart timing of the ON signal is controlled so that the number of theunit display cycles Td1 to Td4 included together with the firstredundant display cycle TD1 is increased or decreased depending on thegradation level.

When the gradation levels 9 to 12 are expressed, the OFF signal isoutputted in synchronization with the respective reset periods Rallotted to the rear end of the second redundant display cycle TD2 andthe followings, and the start timing of the ON signal is controlled sothat the number of the unit display cycles Td1 to Td4 included togetherwith the first and second redundant display cycles TD1 and TD2 isincreased or decreased depending on the gradation level.

When the gradation levels 13 to 16 are expressed, the control is madesuch that the OFF signal is outputted in synchronization with the resetperiod R allotted to the rear end of the one field, and the start timingof the ON signal is controlled so that the number of the unit displaycycles Td1 to Td4 included together with the first to third redundantdisplay cycles TD1 to TD3 is increased or decreased depending on thegradation level.

The sixth and seventh specified embodiments described above areillustrative of the case in which the degree of redundancy n is 4.Alternatively, the present invention is also applicable to the cases inwhich the degree of redundancy n is 2, 3, 5 . . . .

In this case, it is preferable that the unit display cycle and theredundant display cycle are allotted in a combination in which the totalnumber of subfields is minimum, of the total numbers of subfieldscorresponding to the maximum gradation level obtained by arbitrarilycombining the unit display cycle Td and the redundant display cycle TD.

That is, as shown in FIG. 39, the total number of subfields, which isobtained by arbitrarily combining the unit display cycle Td and theredundant display cycle TD, varies depending on the maximum gradationlevel. For example, consideration will be made for the case of thedegree of redundancy n=4 (combination of U(1) and U(4)). In this case,the total number of subfields is 7 when the maximum gradation level is16, and the total number of subfields is 67 when the maximum gradationlevel is 256. In the case of the degree of redundancy n=8 (combinationof U(1) and U(8)), the total number of subfields is 9 when the maximumgradation level is 16, and the total number of subfields is 39 when themaximum gradation level is 256.

Therefore, in this embodiment, when the maximum gradation level is 16,the combination of the degree of redundancy n=4 (combination of U(1) andU(4)), in which the total number of subfields is minimum, is adopted.When the maximum gradation level is 32, the combination of the degree ofredundancy n=4 or 8 (combination of U(1) and U(4) or combination of U(1)and U(U8)) is adopted. Similarly, when the maximum gradation level is64, the combination of the degree of redundancy n=8 is adopted. When themaximum gradation level is 128, the combination of the degree ofredundancy n=8 or 16 (combination of U(1) and U(8) or combination ofU(1) and U(16)) is adopted. When the maximum gradation level is 256, thecombination of the degree of redundancy n=16 is adopted.

By doing so, the total number of subfields is decreased at each of themaximum gradation levels, and it is possible to effectively achieve thereduction of electric power consumption. Further, it is also possible tomitigate the load on the scanning circuit.

The first to seventh specified embodiments are illustrative of thegradation control in which only one cycle of light emission and lightoff is effected for one picture element in one field. Alternatively, asdescribed below in the eighth and ninth specified embodiments, it isalso preferable to perform the gradation control such that two cycles oflight emission and light off are effected for one picture element in onefield.

Eighth Specified Embodiment

As shown in FIG. 40, the eighth specified embodiment is designed asfollows. That is, the first subfield block SFB1 composed of threeredundant display cycles TD1 to TD3 and the second subfield block SFB2composed of four unit display cycles Td1 to Td4 are allotted in the onefield. Further, the forcible reset period TR is allotted between thefirst and second subfield blocks SFB1 and SFB2. The gradation controlsystem used in the eighth specified embodiment is approximately the sameas that used in the second specified embodiment, explanation of which isomitted.

In this embodiment, the redundant display cycle TD is used in the firstsubfield block SFB1. Therefore, it is possible to reduce the number ofrow scanning cycles, and it is possible to realize the reduction ofelectric power consumption. Especially, the provision of the forciblereset period TR makes it possible to give the signal sufficient toquench the picture element during the period described above.

Ninth Specified Embodiment

As shown in FIG. 41, the ninth specified embodiment is constructed inapproximately the same manner as the eighth specified embodiment.However, the former is different from the latter in that two redundantdisplay cycles TD1 and TD2 and one unit display cycle Td are allottedfor the second subfield block SFB2. The gradation control system used inthe ninth specified embodiment is approximately the same as that used inthe second specified embodiment for the first subfield block SFB1, andit is approximately the same as that used in the fifth modifiedembodiment for the second subfield block SFB2, explanation of which isomitted.

In this embodiment, the number of row scanning cycles can be alsoreduced in the second subfield block SFB2. Therefore, it is possible torealize the further reduction of electric power consumption.

The gradation control for the driving devices according to theembodiment of the present invention has been explained above on thebasis of the first to ninth specified embodiments. The driving devicesare preferably used for the arrangement of the display in which thevaristor 120 is connected between the column electrode 28b and thesignal line 42 as shown in FIG. 17, based on the display D according tothe embodiment of the present invention shown in FIG. 1 and the displayDa according to the first modified embodiment shown in FIG. 10.

In this case, as shown in FIG. 42, it is preferable to use −100 V as thepeak value of the selection pulse Ps outputted from the rowelectrode-driving circuit 202, −20 V as the peak value of theunselection signal Su, and 60 V as the peak value of the reset pulse Pr.Further, it is preferable to use 80 V as the ON signal outputted fromthe column electrode-driving circuit 204 and 0 V as the OFF signal.

On the other hand, the driving device according to any one of the firstto ninth specified embodiments may be also used for a display Dfaccording to the sixth modified embodiment as shown in FIG. 43.

The display Df is constructed as follows. That is, the end surface ofthe plate member 32a of the displacement-transmitting section 32contacts with the back surface of the optical waveguide plate 12 at thedistance of not more than the wavelength of the light 10 (lightemission) in the natural state of the actuator element 14 or bysupplying the ON signal to the actuator element 14. When the OFF signalis applied to the actuator element 14, the actuator element 14 makes thebending displacement to be convex toward the hollow space 20, i.e.,makes the bending displacement in the second direction so that the endsurface of the plate member 32a is separated from the optical waveguideplate 12 (light off).

The driving devices according to the first to ninth specifiedembodiments described above are preferably used for the arrangement inwhich the varistor 120 is connected between the column electrode 28b andthe signal line 42 as shown in FIG. 17, based on the display Dfaccording to the sixth modified embodiment shown in FIG. 43.

In this case, as shown in FIG. 44, it is preferable to use 90 V as thepeak value of the selection pulse Ps outputted from the rowelectrode-driving circuit 202, −10 V as the peak value of theunselection signal Su, and −110 V as the peak value of the reset pulsePr. Further, it is preferable to use 0 V as the ON signal outputted fromthe column electrode-driving circuit 204 and 100 V as the OFF signal.

More preferably, as shown in FIG. 45, it is appropriate to use 170 V asthe peak value of the selection pulse Ps outputted from the rowelectrode-driving circuit 202, 0 V as the peak value of the unselectionsignal Su, and −160 V as the peak value of the reset pulse Pr. Further,it is appropriate to use 0 V as the ON signal outputted from the columnelectrode-driving circuit 204 and 80 V as the OFF signal.

Additionally, in the first to ninth specified embodiments concerning thedriving device according to the embodiment of the present invention, theelectric power consumption can be further reduced by using an electricpower recovery circuit in combination.

The gradation control effected in the driving device as described aboveis also applicable to the gradation control used for the liquid crystaldisplay and the plasma display.

For example, in the case of the plasma display, each of the pictureelements (discharge cells) is represented by a capacitive element(capacitor) by using an equivalent circuit, thus providing the memoryeffect in the same manner as the respective picture elements, of thedisplay according to the embodiment of the present invention. Therefore,the gradation control for the driving device according to the embodimentof the present invention can be applied thereto.

In this case, the following effects can be obtained.

(1) It is possible to realize the high brightness, because the longlight emission maintenance period is available.

(2) It is possible to avoid occurrence of so-called pseudo-contour,because the gradational expression is not performed by using thecombination of divided subfields.

(3) It is possible to lower the electric power consumption, because onlyone time (first to seventh specified embodiments) or two times (eighthand ninth specified embodiments) of light-on discharge is provided inone field.

The gradation control according to the embodiment of the presentinvention is also applicable to TFT-LCD (liquid crystal display based onthe active matrix system), because TFT-LCD lies in the combination ofthe switching element and the capacitive picture element. In this case,it is possible to realize the high brightness and the low electric powerconsumption.

The gradation control according to the embodiment of the presentinvention (especially, those concerning the second, third, fifth,eighth, and ninth specified embodiments) is also applicable to LCD basedon the simple matrix system by utilizing the frame response of thepicture element. FIG. 46 shows a frame response waveform in which thesecond specified embodiment (see FIGS. 33A to 33C) concerning theembodiment of the present invention is applied to LCD based on thesimple matrix system to express the gradation level=7.

In FIG. 46, S/ON indicates a state in which the ON signal is outputtedduring the selection period for the selected picture element, S/OFFindicates a state in which the OFF signal is outputted during theselection period for the concerning picture element, and R/OFF indicatesa state in which the OFF signal is outputted during the reset period forthe concerning picture element. Therefore, in the example shown in FIG.46, the light emission maintenance period ranges from the point of timeof S/ON to the point of time of R/OFF.

In the display D according to the embodiment of the present invention,for example, as shown in FIG. 1, the light off is effected in thenatural state of the actuator element 14, and the light emission iseffected by allowing the actuator element 14 to make the bendingdisplacement to be convex toward the optical waveguide plate 12 when thehigh level voltage is applied between the row electrode 28a and thecolumn electrode 28b of the actuator element 14. Alternatively, it isalso preferable that the static electricity is generated between theback surface of the optical waveguide plate 12 and the contact surface(end surface) of the displacement-transmitting section 32, in additionto the strain generated by applying the voltage to the shape-retaininglayer 26 when the actuator element 14 is subjected to the ONoperation/OFF operation by allowing the displacement-transmittingsection 32 to make contact/separation with respect to the back surfaceof the optical waveguide plate 12, so that the attractive force and therepulsive force brought about by the static electricity may be utilizedfor the ON operation/OFF operation of the actuator element 14.

As a result, the following arrangement is available. That is, thedielectric polarization is caused during the operation of the actuatorelement 14 to improve the ON characteristic of the actuator element 14(for example, the contact performance and the response performance inthe contact direction of the displacement-transmitting section 32) byutilizing the attractive force brought about by the static electricity.Further, it is also possible to improve the OFF characteristic (forexample, the separation performance and the response performance in theseparation direction of the displacement-transmitting section 32) inaddition to the ON characteristic of the actuator element 14 byutilizing not only the attractive force but also the repulsive forcebrought about by the static electricity.

For example, when it is intended to improve only the ON characteristicof the actuator element 14, a coating material is merely arranged on thecontact surface (end surface) of the displacement-transmitting section32 and the optical waveguide plate 12 itself or the back surface of theoptical waveguide plate 12 to allow them to cause the dielectricpolarization.

Further, for example, when it is intended to improve both of the ONcharacteristic and the OFF characteristic of the actuator element 14, atransparent electrode or a metal thin film is arranged on the backsurface of the optical waveguide plate 12 to switch the electricpolarity thereof so that both of the attractive force and the repulsiveforce are generated by the static electricity with respect to thecontact surface of the displacement-transmitting section 32 subjected tothe dielectric polarization.

The arrangement described above will be specifically explained withreference to FIGS. 47A to 48B. The display D is constructed such thatthe actuator element 14 is allowed to cause light emission in thenatural state, the row electrode 28a is formed on the upper surface ofthe shape-retaining layer 26, and the column electrode 28b is formed onthe lower surface of the shape-retaining layer 26 as shown in FIGS. 47Aand 47B. In this display D, transparent electrodes 290 are formed atpositions of the back surface of the optical waveguide plate 12corresponding to the actuator elements 14 respectively.

When the actuator element 14 is subjected to the ON operation to causethe light emission, for example, as shown in FIG. 47A, then the voltage(Vc>Va) is applied between the row electrode 28a and the transparentelectrode 290 corresponding to the concerning actuator element 14, andthe voltage between the row electrode 28a and the column electrode 28bis made approximately zero (Va≈Vb).

Accordingly, the displacement-transmitting section 32 is pressed towardthe optical waveguide plate 12 in accordance with the electrostaticattractive force exerted between the transparent electrode 290 and therow electrode 28a. The pressing force makes it possible to improve thebrightness and improve the response speed.

On the other hand, when the actuator element 14 is subjected to the OFFoperation to cause the light off, as shown in FIG. 47B, then the voltagebetween the row electrode 28a and the transparent electrode 290corresponding to the concerning actuator element 14 is madeapproximately zero (Vc≈Va), and the voltage (Va<Vb) is applied betweenthe row electrode 28a and the column electrode 28b.

Accordingly, the actuator element 14 makes bending displacement to beconvex toward the hollow space 20, and the displacement-transmittingsection 32 is separated from the optical waveguide plate 12.

The transparent electrode 290 may be formed on any of the back surfaceof the optical waveguide plate 12 and the end surface of thedisplacement-transmitting section 32. However, the transparent electrode290 is preferably formed on the end surface of thedisplacement-transmitting section 32 because of the following reason.That is, the distance between the transparent electrode 290 and the rowelectrode 28a on the actuator element 14 is decreased, and it ispossible to generate larger electrostatic force.

The transparent electrode 290, which is formed on the back surface ofthe optical waveguide plate 12, is effective to improve the separationperformance of the displacement-transmitting section 32. In general, thelocal surface electric charge is generated on thedisplacement-transmitting section 32 and the optical waveguide plate 12in accordance with the contact and separation of thedisplacement-transmitting section 32. The local surface electric chargeassists the displacement-transmitting section 32 to make contact withthe optical waveguide plate 12. However, in such a situation, aninconvenience tends to occur such that the displacement-transmittingsection 32 adheres to the optical waveguide plate.

Accordingly, when the transparent electrode 290 is formed on the backsurface of the optical waveguide plate 12, then the generation of thelocal surface electric charge Is mitigated, the inconvenience (adhesion)is reduced, and the separation performance of thedisplacement-transmitting section 32 is improved.

The arrangement, in which the transparent electrode 290 is formed toutilize the static electricity, is also applicable to the display D asshown in FIGS. 48A and 48B, i.e., the display D including the pair ofelectrodes (the row electrode 28a and the column electrode 28b) formedon the upper surface of the shape-retaining layer 26.

That is, the transparent electrode 290 is formed on the back surface ofthe optical waveguide plate 12. When the voltage (Vc>Va, Vc>Vb) isapplied between the transparent electrode 290 and the pair of electrodes28a, 28b provided on the upper surface of the actuator element 14, thestatic electricity is generated between the both.

In this arrangement, it is assumed that the actuator element 14 issubjected to light off in the natural state. When the concerningactuator element 14 is subjected to the ON operation to cause lightemission, then the voltage (Va<Vb<Vc) between the pair of electrodes28a, 28b allows the actuator element 14 to make the bending displacementtoward the optical waveguide plate 12, and the attractive force of thestatic electricity causes the displacement-transmitting section 32 toquickly approach the optical waveguide plate 12. Thus, the lightemission state is given. On the contrary, in the state in which novoltage is applied between the transparent electrode 290 and the pair ofelectrodes 28a, 28b (Va≈Vb≈Vc), then the actuator element 14 issubjected to the OFF operation, and it is separated from the opticalwaveguide plate 12 in accordance with the rigidity of the actuatorelement 14. Thus, the light off state is given.

The driving systems according to the first to ninth specifiedembodiments are also applicable to the display D based on the use of thestatic electricity as described above.

It is a matter of course that.the display-driving device and thedisplay-driving method according to the present invention are notlimited to the embodiments described above, which may be embodied inother various forms without deviating from the gist or essentialcharacteristics of the present invention.

As explained above, according to the display-driving device and thedisplay-driving method concerning the present invention, it is possibleto effectively reduce the electric power consumption, and it is possibleto achieve the high brightness. Further, it is possible to effectivelyreduce the electric power consumption, and it is possible to achieve thehigh brightness in the gradation control based on the subfield driving.It is possible to reduce the total number of subfield, and it ispossible to effectively reduce the electric power consumption in thegradation control based on the subfield driving.

1. A display-driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display-driving device comprising: a first driving circuit for selecting said picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein: a display period for one image is defined as one field, and in order to perform gradation control based on a temporal modulation system, said signal control circuit determines, in said one field, a light emission start timing and a contiguous light emission maintenance period having a variable length, independent of a selection/unselection state of a predetermined picture element, depending on a gradation level of said predetermined picture element, wherein said contiguous light emission maintenance period is provided by a memory function of said predetermined picture element.
 2. The display-driving device according to claim 1, wherein: one selection period and display cycles of a number corresponding to a maximum gradation level are allotted in said one field; each of said display cycles is composed of an unselection period and a reset period; and said signal control circuit is operated such that said predetermined picture element is in a light emission state when said ON signal indicating light emission is inputted during said selection period, or said predetermined picture element is in a light off state when said OFF signal indicating light off is inputted during said reset period in said display cycle.
 3. The display-driving device according to claim 2, wherein: signal levels are determined for said unselection period and said reset period so that said light emission state of said predetermined picture element is maintained during said light emission maintenance period; and signal levels are determined for said selection period and said unselection period so that said light off state of said predetermined picture element is maintained during any period other than said light emission maintenance period.
 4. The display-driving device according to claim 1, wherein: display cycles of a number corresponding to a maximum gradation level and one reset period are allotted in said one field; each of said display cycles is composed of a selection period and an unselection period; and said signal control circuit is operated such that said predetermined picture element is in a light emission state when said ON signal indicating light emission is inputted during said selection period, or said predetermined picture element is in a light off state during said reset period.
 5. The display-driving device according to claim 4, wherein signal levels are determined for said selection period and said unselection period so that said light emission state of said predetermined picture element is maintained during said light emission maintenance period.
 6. The display-driving device according to claim 1, wherein: an odd/even-adjusting cycle including a unit unselection period having a predetermined length between two selection periods, and display cycles of a number corresponding to a maximum gradation level are allotted in said one field; and each of said display cycles is provided with a redundant unselection period having a length which is twice said predetermined length and a reset period.
 7. The display-driving device according to claim 6, wherein: when said gradation level of said predetermined picture element is odd, said light emission start timing is set to be substantially in synchronization with said a head selection period of said odd/even-adjusting cycle; while when said gradation level of said predetermined picture element is even, said light emission start timing is set to be substantially in synchronization with said a rear end selection period of said odd/even-adjusting cycle.
 8. The display-driving device according to claim 1, wherein: display cycles of a number corresponding to a maximum gradation level, and an odd/even-adjusting cycle including a unit unselection period having a predetermined length between two reset periods are allotted in said one field; and each of said display cycles is provided with a selection period and a redundant unselection period having a length which is twice said predetermined length.
 9. The display-driving device according to claim 8, wherein: when said gradation level of said predetermined picture element is odd, an end timing for said light emission maintenance period is set to be substantially in synchronization with said a terminal end reset period of said odd/even-adjusting cycle; while when said gradation level of said predetermined picture element is even, said end timing for said light emission maintenance period is set to be substantially in synchronization with said a head reset period of said odd/even-adjusting cycle.
 10. The display-driving device according to claim 1, wherein: at least one unit display cycle including a unit unselection period having a predetermined length, and at least one redundant display cycle are allotted in said one field; and said redundant display cycle is provided with a redundant unselection period having a length which is n-times said predetermined length provided that n is an integer of not less than
 2. 11. The display-driving device according to claim 10, wherein the following expressions are satisfied: Z=(quotient of X/n)−1 Y=X−Z×n total number of subfields (Y+Z)=(X/n−1)+n provided that a maximum gradation level is X, a number of unit display cycles is Y, and a number of redundant display cycles is Z.
 12. The display-driving device according to claim 11, wherein “a” individuals of selection periods are allotted to said respective display cycles from a head of said one field, and “b” individuals of reset periods are allotted to said respective display cycles from a rear end of said one field, and wherein following expression is satisfied: a+b=Y+Z+1.
 13. The display-driving device according to claim 10, wherein said unit display cycle and said redundant display cycle are allotted by using a combination which corresponds to a minimum total number of subfields of total numbers of subfields corresponding to a maximum gradation level obtained by arbitrarily combining said unit display cycle and said redundant display cycle.
 14. The display-driving device according to claim 10, wherein: said one field includes therein a first subfield block composed of at least one redundant display cycle and a second subfield block composed of at least one unit display cycle; and a forcible reset period is provided between said first and second subfield blocks.
 15. The display-driving device according to claim 14, wherein said second subfield block is composed of at least one redundant display cycle and at least one unit display cycle.
 16. The display-driving device according to claim 1, wherein said display comprises an optical waveguide plate for introducing light thereinto, and said driving section provided opposingly to one plate surface of said optical waveguide plate and including a number of actuator elements arranged corresponding to said large number of picture elements, for displaying, on said optical waveguide plate, said picture image corresponding to said image signal by controlling leakage light at a predetermined portion of said optical waveguide plate by controlling displacement action of each of said actuator elements in a direction to make contact or separation with respect to said optical waveguide plate in accordance with an attribute of said image signal to be inputted.
 17. The display-driving device according to claim 16, wherein: said actuator element comprises a shape-retaining layer, an operating section having at least a pair of electrodes formed on said shape-retaining layer, a vibrating section for supporting said operation section, and a fixed section for supporting said vibrating section in a vibrating manner; and said display comprises a displacement-transmitting section for transmitting said displacement action of said actuator element to said optical waveguide plate, said displacement action being generated by voltage application to said pair of electrodes.
 18. The display-driving device according to claim 16, wherein: said driving section is formed with switching elements corresponding to said actuator elements respectively; and said displacement action of said actuator element is controlled by means of ON/OFF control effected by said switching element.
 19. The display-driving device according to claim 18, wherein said switching element is composed of a varistor.
 20. The display-driving device according to claim 17, wherein said shape-retaining layer is a piezoelectric/electrostrictive layer.
 21. The display-driving device according to claim 17, wherein said shape-retaining layer is an anti-ferroelectric layer.
 22. A display-driving method for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal; said display-driving method comprising the step of: selecting said picture elements at least in one row unit; outputting display information composed of an ON signal and an OFF signal to a selected row; and performing gradation control based on a temporal modulation system, wherein: a display period for one image is defined as one field, a light emission start timing and a contiguous light emission maintenance period having a variable length, independent of a selection/unselection state of a predetermined picture element, are determined in said one field depending on a gradation level of said predetermined picture element, and wherein said contiguous light emission maintenance period is provided by a memory function of said predetermined picture element.
 23. The display-driving method according to claim 22, wherein: one selection period and display cycles of a number corresponding to a maximum gradation level are allotted in said one field; each of said display cycles is composed of an unselection period and a reset period; and said predetermined picture element is in a light emission state when said ON signal indicating light emission is inputted during said selection period; or said predetermined picture element is in a light off state when said OFF signal indicating light off is inputted during said reset period in said display cycle.
 24. The display-driving method according to claim 23, wherein: signal levels are determined for said unselected period and said reset period so that said light emission state of said predetermined picture element is maintained during said light emission maintenance period; and signal levels are determined for said selection period and said unselection period so that said light off state of said predetermined picture element is maintained during any period other than said light emission maintenance period.
 25. The display-driving method according to claim 22, wherein: display cycles of a number corresponding to a maximum gradation level and one reset period are allotted in said one field; each of said display cycles is composed of a selection period and an unselection period; and said predetermined picture element is in a light emission state when said ON signal indicating light emission is inputted during said selection period; or said predetermined picture element is in a light off state during said reset period.
 26. The display-driving method according to claim 25, wherein signal levels are determined for said selection period and said unselection period so that said light emission state of said predetermined picture element is maintained during said light emission maintenance period.
 27. The display-driving method according to claim 22, wherein: an odd/even-adjusting cycle including a unit unselection period having a predetermined length between two selection periods, and display cycles of a number corresponding to a maximum gradation level are allotted in said one field; and each of said display cycles is provided with a redundant unselection period having a length which is twice said predetermined length and a reset period.
 28. The display-driving method according to claim 27, wherein: when said gradation level of said predetermined picture element is odd, said light emission start timing is set to be substantially in synchronization with said a head selection period of said odd/even-adjusting cycle; while when said gradation level of said predetermined picture element is even, said light emission start timing is set to be substantially in synchronization with said a rear end selection period of said odd/even-adjusting cycle.
 29. The display-driving method according to claim 22, wherein: display cycles of a number corresponding to a maximum gradation level, and an odd/even-adjusting cycle including a unit unselection period having a predetermined length between two reset periods are allotted in said one field; and each of said display cycles is provided with a selection period and a redundant unselection period having a length which is twice said predetermined length.
 30. The display-driving method according to claim 29, wherein: when said gradation level of said predetermined picture element is odd, an end timing for said light emission maintenance period is set to be substantially in synchronization with said a terminal end reset period of said odd/even-adjusting cycle; while when said gradation level of said predetermined picture element is even, said end timing for said light emission maintenance period is set to be substantially in synchronization with said a head reset period of said odd/even-adjusting cycle.
 31. The display-driving method according to claim 22, wherein: at least one unit display cycle including a unit unselection period having a predetermined length, and at least one redundant display cycle are allotted in said one field; and said redundant display cycle is provided with a redundant unselection period having a length which is n-times said predetermined length provided that n is an integer of not less than
 2. 32. The display-driving method according to claim 31, wherein the following expressions are satisfied: Z=(quotient of X/n)−1 Y=X−Z×n total number of subfields (Y+Z)=(X/n−1)+n provided that a maximum gradation level is X, a number of unit display cycles is Y, and a number of redundant display cycles is Z.
 33. The display-driving method according to claim 32, wherein: “a” individuals of selection periods are allotted to said respective display cycles from a head of said one field, and “b” individuals of reset periods are allotted to said respective display cycles from a rear end of said one field, and wherein following expression is satisfied: a+b=Y+Z+1.
 34. The display-driving method according to claim 31, wherein said unit display cycle and said redundant display cycle are allotted by using a combination which corresponds to a minimum total number of subfields of total members of subfields corresponding to a maximum gradation level obtained by arbitrarily combining said unit display cycle and said redundant display cycle.
 35. The display-driving method according to claim 31, wherein: said one field includes therein a first subfield block composed of at least one redundant display cycle and a second subfield block composed of at least one unit display cycle; and a forcible reset period is provided between said first and second subfield blocks.
 36. The display-driving method according to claim 35, wherein said second subfield block is composed of at least one redundant display cycle and at least one unit display cycle.
 37. The display-driving method according to claim 22, wherein said gradation control is performed for said picture element by means of ON/OFF control effected by a switching element.
 38. The display-driving method according to claim 37, wherein a varistor is used as said switching element.
 39. A display-driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display-driving device comprising: a first driving circuit for selecting said picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein: a display period for one image is defined as one field, and in order to perform gradation control based on at least a temporal modulation system, said signal control circuit determines, in said one field, a light emission start timing and a light emission maintenance period having a variable length, independent of a selection/unselection state of a predetermined picture element, depending on a gradation level of said predetermined picture element; at least one unit display cycle including a unit unselection period having a predetermined length and at least one redundant display cycle are allotted in said one field, said redundant display cycle being provided with a redundant unselection period having a length which is n-times said predetermined length provided that n is an integer of not less than 2; and the following expressions are satisfied: Z=(quotient of X/n)−1 Y=X−Z×n total number of subfields (Y+Z)=(X/n−1)+n  provided that a maximum gradation level is X, a number of unit display cycles is Y, and a number of redundant display cycles is Z.
 40. The display-driving device according to claim 39, wherein “a” individuals of selection periods are allotted to said respective display cycles from a head of said one field, and “b” individuals of reset periods are allotted to said respective display cycles from a rear end of said one field, and wherein following expression is satisfied: a+b=Y+Z+1.
 41. A display-driving method for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal; said display-driving method comprising the step of: selecting said picture elements at least in one row unit; outputting display information composed of an ON signal and an OFF signal to a selected row; and performing gradation control based on at least a temporal modulation system, wherein: a display period for one image is defined as one field, a light emission start timing and a light emission maintenance period having a variable length, independent of a selection/unselection state of a predetermined picture element, are determined in said one field depending on a gradation level of said predetermined picture element; at least one unit display cycle including a unit unselection period having a predetermined length and at least one redundant display cycle are allotted in said one field, said redundant display cycle being provided with a redundant unselection period having a length which is n-times said predetermined length provided that n is an integer of not less than 2; and the following expressions are satisfied: Z=(quotient of X/n)−1 Y=X−Z×n total number of subfields (Y+Z)=(X/n−1)+n  provided that a maximum gradation level is X, a number of unit display cycles is Y, and a number of redundant display cycles is Z.
 42. The display-driving method according to claim 41, wherein: “a” individuals of selection periods are allotted to said respective display cycles from a head of said one field, and “b” individuals of reset periods are allotted to said respective display cycles from a rear end of said one field, and wherein the following expression is satisfied: a+b=Y+Z+1.
 43. A display-driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display driving device comprising: a first driving circuit for selecting picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein: a display period for one image is defined as one field, and in order to perform gradation control based on a temporal modulation system, said signal control circuit turns a predetermined picture element ON only once in said one field and turns said picture element OFF only once in said one field, and the ON/OFF state of said picture element is maintained by a memory function of said picture element.
 44. The display-driving device according to claim 43 wherein: a plurality of display cycles are allotted in said one field; said picture element is turned ON only in a first display cycle in said one field; and said picture element is turned OFF in one of said display cycles other than said first display cycle in said one field.
 45. The display-driving device according to claim 44 , wherein: said display cycles other than said first display cycle have a row scanning period for performing row selection in order to input a control signal to turn said picture element OFF; and the ON/OFF state of said picture element is maintained in an unselection period of the row which includes said picture element in said row scanning period.
 46. The display-driving device according to claim 43 , wherein: a plurality of display cycles are allotted in said one field; said picture element is turned OFF only in a last display cycle in said one field; and said picture element is turned ON in one of said display cycles other than said last display cycle in said one field.
 47. The display-driving device according to claim 46 , wherein: said display cycles other than said last display cycle have a row scanning period for performing row selection in order to input a control signal to turn said picture element ON; and the ON/OFF state of said picture element is maintained in an unselection period of the row which includes said picture element in said row scanning period.
 48. The display-driving device according to claim 43 , wherein: a plurality of display cycles are allotted in said one field; and said picture element is turned ON in one of said display cycles and turned OFF in another of said display cycles.
 49. The display-driving device according to claim 48 , wherein: said display cycles have a row scanning period for performing row selection in order to input a control signal to turn said picture element ON or OFF; and the ON/OFF state of said picture element is maintained in an unselection period of the row which includes said picture element in said row scanning period.
 50. A display-driving method for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display driving method comprising the steps of: selecting picture elements at least in one row unit; outputting display information composed of an ON signal and an OFF signal to a selected row; and performing gradation control based on a temporal modulation system, wherein: a display period for one image is defined as one field, and said signal control circuit turns a predetermined picture element ON only once in said one field and turns said picture element OFF only once in said one field, and the ON/OFF state of said picture element is maintained by a memory function of said picture element.
 51. The display-driving method according to claim 50 , wherein: a plurality of display cycles are allotted in said one field; said picture element is turned ON only in a first display cycle in said one field; and said picture element is turned OFF in one of said display cycles other than said first display cycle in said one field.
 52. The display-driving method according to claim 51 , wherein: said display cycles other than said first display cycle have a row scanning period for performing row selection in order to input a control signal to turn said picture element OFF; and the ON/OFF state of said picture element is maintained in an unselection period of the row which includes said picture element in said row scanning period.
 53. The display-driving device according to claim 50 , wherein: a plurality of display cycles are allotted in said one field; said picture element is turned OFF only in a last display cycle in said one field; and said picture element is turned ON in one of said display cycles other than said last display cycle in said one field.
 54. The display-driving method according to claim 53 , wherein: said display cycles other than said last display cycle have a row scanning period for performing row selection in order to input a control signal to turn said picture element ON; and the ON/OFF state of said picture element is maintained in an unselection period of the row which includes said picture element in said row scanning period.
 55. The display-driving method according to claim 50 , wherein: a plurality of display cycles are allotted in said one field; and said picture element is turned ON in one of said display cycles and turned OFF in another of said display cycles.
 56. The display-driving method according to claim 55 , wherein: said display cycles have a row scanning period for performing row selection in order to input a control signal to turn said picture element ON or OFF; and the ON/OFF state of said picture element is maintained in an unselection period of the row which includes said picture element in said row scanning period.
 57. A display driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display driving device comprising: a first driving circuit for selecting picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein: a display period for one image is defined as one field and a first display cycle group and a second display cycle group are allotted in said one field, said first and second display cycle groups comprising one display cycle or at least two continuously allotted display cycles, wherein each of said first and second display cycle groups are arranged in a different period within said one field and said second display cycle group is arranged following said first display cycle group, and in order to perform gradation control based on a temporal modulation system, a predetermined picture element is turned ON in only one of said display cycles in said first display cycle group and the ON state of said picture element is maintained by a memory function of said picture element until said picture element is turned OFF in only one of said display cycles in said second display cycle group.
 58. A display-driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display driving device comprising: a first driving circuit for selecting picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein: a display period for one image is defined as one field and a first display cycle group and a second display cycle group are allotted in said one field, said first and second display cycle groups comprising one display cycle or at least two continuously allotted display cycles, wherein each of said first and second display cycle groups are arranged in a different period within said one field and said second display cycle group is arranged following said first display cycle group, and in order to perform gradation control based on a temporal modulation system, a predetermined picture element is turned ON in one of said display cycles in said first display cycle group and the ON state of said picture element is maintained by a memory function of said picture element until said picture element is turned OFF in one of said display cycles in said second display cycle group, wherein said display cycles at least in said second display cycle group have a row scanning period for performing row selection in order to input a control signal to turn said picture element OFF, and wherein said picture element emits light in the ON state until the end of said row scanning period.
 59. A display driving method for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display driving method comprising the steps of: selecting picture elements at least in one row unit; and outputting display information composed of an ON signal and an OFF signal to a selected row, wherein a display period for one image is defined as one field and a first display cycle group and a second display cycle group are allotted in said one field, said first and second display cycle groups comprising one display cycle or at least two continuously allotted display cycles, wherein each of said first and second display cycle groups are arranged in a different period within said one field and said second display cycle group is arranged following said first display cycle group, and in order to perform gradation control based on a temporal modulation system, a predetermined picture element is turned ON in only one of said display cycles in said first display cycle group and the ON state of said picture element is maintained by a memory function of said picture element until said picture element is turned OFF in only one of said display cycles in said second display cycle group.
 60. A display-driving method for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display driving method comprising the steps of: selecting picture elements at least in one row unit; and outputting display information composed of an ON signal and an OFF signal to a selected row, wherein a display period for one image is defined as one field and a first display cycle group and a second display cycle group are allotted in said one field, said first and second display cycle groups comprising one display cycle or at least two continuously allotted display cycles, wherein each of said first and second display cycle groups are arranged in a different period within said one field and said second display cycle group is arranged following said first display cycle group, and in order to perform gradation control based on a temporal modulation system, a predetermined picture element is turned ON in one of said display cycles in said first display cycle group and the ON state of said picture element is maintained by a memory function of said picture element until said picture element is turned OFF in one of said display cycles in said second display cycle group, wherein said display cycles at least in said second display cycle group have a row scanning period for performing row selection in order to input a control signal to turn said picture element OFF, and wherein said picture element emits light in the ON state until the end of said row scanning period.
 61. A display-driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display driving device comprising: a first driving circuit for selecting picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein: a display period for one image is defined as one field and a first display cycle group and a second display cycle group are allotted in said one field, said first and second display cycle groups comprising one display cycle or at least two continuously allotted display cycles, wherein said second display cycle group is arranged following said first display cycle group, and in order to perform gradation control based on a temporal modulation system, a predetermined picture element is turned ON in one of said display cycles in said first display group and the ON state of said picture element is maintained by a memory function of said picture element until said picture element is turned OFF in one of said display cycles in said second display cycle group, wherein said display cycles at least in said second display cycle group have a row scanning period for performing row selection in order to input a control signal to turn said picture element OFF, and wherein said picture element emits light in the ON state until the end of said row scanning period.
 62. A display-driving method for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display driving method comprising the steps of: selecting picture elements at least in one row unit; outputting display information composed of an ON signal and an OFF signal to a selected row, wherein a display period for one image is defined as one field and a first display cycle group and a second display cycle group are allotted in said one field, said first and second display cycle groups comprising one display cycle or at least two continuously allotted display cycles, wherein said second display cycle group is arranged following said first display cycle group, and in order to perform gradation control based on a temporal modulation system, said picture element is turned ON in one of said display cycles in said first display cycle group and the ON state of said picture element is maintained by a memory function of said picture element until said picture element is turned OFF in one of said display cycles in said second display cycle group, wherein said display cycles at least in said second display cycle group have a row scanning period for performing row selection in order to input a control signal to control whether to turn said picture element OFF, and wherein said picture element emits light in the ON state until the end of said row scanning period.
 63. A display-driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display-driving device comprising: a first driving circuit for selecting said picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein: a display period for one image is defined as one field, and in order to perform gradation control based on a temporal modulation system, said signal control circuit determines, in said one field, a contiguous light emission maintenance period having a variable length, independent of a selection/unselection state of a predetermined picture element, depending on a gradation level of said predetermined picture element.
 64. A display-driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display-driving device comprising: a first driving circuit for selecting said picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein: a display period for one image is defined as one field, and in order to perform gradation control based on a temporal modulation system, said signal control circuit determines, in said one field, a light emission start timing and a contiguous light emission maintenance period having a variable length, independent of a selection/unselection state of a predetermined picture element, depending on a gradation level of said predetermined picture element, wherein said light emission start timing is fixed in said one field.
 65. A display-driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display-driving device comprising: a first driving circuit for selecting said picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein: a display period for one image is defined as one field, and in order to perform gradation control based on a temporal modulation system, said signal control circuit determines, in said one field, a light emission start timing and a contiguous light emission maintenance period having a variable length, independent of a selection/unselection state of a predetermined picture element, depending on a gradation level of said predetermined picture element, wherein said light emission start timing is variable in said one field.
 66. A display-driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal, said display-driving device comprising: a first driving circuit for selecting said picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling said first and second driving circuits, wherein: a display period for one image is defined as one field, and in order to perform gradation control based on a temporal modulation system, said signal control circuit determines, in said one field, a light emission start timing and a contiguous ON state period having a variable length, indepnednet of a selection/unselection state of a predetermined picture element, depending on a gradation level of said predetermined picture element. 